Transmitting trigger frame in wireless local area network and wireless terminal using the same

ABSTRACT

A method for transmitting a trigger frame performed by a first wireless terminal may include, configuring a trigger frame of a basic type including a plurality of user information fields for an OFDMA-based random access backoff procedure by a plurality of second wireless terminals, wherein each of the plurality of user information fields includes resource allocation information for a RA resource unit allocated for the OFDMA-based random access backoff procedure, identifier information indicating that the RA resource unit is allocated for the OFDMA-based random access backoff procedure, and TID aggregation limit information indicating the maximum number of TIDs allowed for an A-MPDU generated by a second wireless terminal that has completed the OFDMA random access backoff procedure based on the trigger frame, and wherein the TID aggregation limit information is set to 0 or 1; and transmitting the trigger frame to the plurality of second wireless terminals.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(e), this application claims the benefit ofU.S. Provisional Patent Application No. 62/509,710, filed on May 22,2017, 62/519,867, filed on Jun. 15, 2017, 62/525,173, filed on Jun. 26,2017 and 62/525,177, filed on Jun. 26, 2017, the contents of which areall hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present specification relates to wireless communication and, moreparticularly, to a method for transmitting a trigger frame in a wirelesslocal area network (WLAN) system, and a wireless terminal using thesame.

Related Art

A next-generation WLAN is aimed at 1) improving Institute of Electricaland Electronics Engineers (IEEE) 802.11 physical (PHY) and medium accesscontrol (MAC) layers in bands of 2.4 GHz and 5 GHz, 2) increasingspectrum efficiency and area throughput, and 3) improving performance inactual indoor and outdoor environments, such as an environment in whichan interference source exists, a dense heterogeneous networkenvironment, and an environment in which a high user load exists.

In the next-generation WLAN, a dense environment having a great numberof access points (APs) and stations (STAs) is primarily considered.Discussions have been conducted on improvement in spectrum efficiencyand area throughput in this dense environment. The next-generation WLANpays attention to actual performance improvement not only in an indoorenvironment but also in an outdoor environment, which is notsignificantly considered in the existing WLAN.

Specifically, scenarios for a wireless office, a smart home, a stadium,a hotspot, and the like receive attention in the next-generation WLAN.Discussions are ongoing on improvement in the performance of a WLANsystem in the dense environment including a large number of APs and STAsbased on relevant scenarios.

In the next-generation WLAN, improvement of system performance in anoverlapping basic service set (OBSS) environment and improvement ofoutdoor environment performance, and cellular offloading are expected tobe more actively discussed rather than the improvement of single linkperformance in one basic service set (BSS). Directionality of thenext-generation means that the next-generation WLAN is graduallyachieving a technical scope that is similar to that of mobilecommunication. Considering the recent situation wherein discussions havebeen made on the mobile communication and WLAN technology in areas ofsmall cells and direct-to-direct (D2D) communication area, technical andbusiness convergence of the next-generation WLAN and the mobilecommunication is predicted to be more active in the future.

SUMMARY OF THE INVENTION

A method for transmitting a trigger frame in a wireless local areanetwork system according to an embodiment may include: configuring, bythe first wireless terminal, a trigger frame of a basic type including aplurality of user information fields for an OFDMA-based random accessbackoff procedure by a plurality of second wireless terminals, each ofthe plurality of user information fields including: resource allocationinformation for a random access (RA) resource unit allocated for theOFDMA-based random access backoff procedure; identifier informationindicating that the RA resource unit is allocated for the OFDMA-basedrandom access backoff procedure; and TID aggregation limit informationindicating the maximum number of TIDs allowed for an A-MPDU generated bya second wireless terminal that has completed the OFDMA random accessbackoff procedure on the basis of the trigger frame among the pluralityof second wireless terminals, and the TID aggregation limit informationbeing set to 0 or 1; and transmitting, by the first wireless terminal,the trigger frame to the plurality of second wireless terminals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

FIG. 4 is a diagram illustrating a layout of resource units used in aband of 20 MHz.

FIG. 5 is a diagram illustrating a layout of resource units used in aband of 40 MHz.

FIG. 6 is a diagram illustrating a layout of resource units used in aband of 80 MHz.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B.

FIG. 9 illustrates an example of a trigger frame.

FIG. 10 illustrates an example of a sub-field included in a per userinformation field.

FIG. 11 illustrates an example of a sub-field being included in a peruser information.

FIG. 12 is a diagram illustrating an EDCA-based channel access method ina WLAN system.

FIG. 13 is a conceptual view illustrating a backoff procedure of anEDCA.

FIG. 14 is a diagram describing a transmission procedure of a frame in aWLAN system.

FIG. 15 illustrates an example of a MAC frame.

FIG. 16 is a conceptual view illustrating a frame structure of an MPDUthat is generated based on a plurality of MSDUs according to anembodiment.

FIG. 17 is a conceptual view illustrating a frame structure of anA-MPDU, wherein a plurality of MPDUs is aggregated, according to anembodiment.

FIG. 18 is a diagram illustrating a field of a basic trigger frameincluding preference information and limit information according to anembodiment.

FIG. 19 illustrates an OFDMA-based random access procedure according toan embodiment.

FIG. 20 is a flowchart illustrating a method for transmitting a triggerframe in a WLAN system according to an embodiment.

FIG. 21 is a block diagram illustrating a wireless device according toan embodiment.

FIG. 22 is a block diagram illustrating an example of a device includedin a processor.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The aforementioned features and following detailed descriptions areprovided for exemplary purposes to facilitate explanation andunderstanding of the present specification. That is, the presentspecification is not limited to such an embodiment and thus may beembodied in other forms. The following embodiments are examples only forcompletely disclosing the present specification and are intended toconvey the present specification to those ordinarily skilled in the artto which the present specification pertain. Therefore, where there areseveral ways to implement constitutional elements of the presentspecification, it is necessary to clarify that the implementation of thepresent specification is possible by using a specific method among thesemethods or any of its equivalents.

When it is mentioned in the present specification that a certainconfiguration includes particular elements, or when it is mentioned thata certain process includes particular steps, it means that otherelements or other steps may be further included. That is, theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to limit the concept of thepresent specification. Further, embodiments described to helpunderstanding of the invention also includes complementary embodimentsthereof.

Terms used in the present specification have the meaning as commonlyunderstood by those ordinarily skilled in the art to which the presentspecification pertains. Commonly used terms should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthe present specification. Further, terms used in the presentspecification should not be interpreted in an excessively idealized orformal sense unless otherwise defined. Hereinafter, an embodiment of thepresent specification is described with reference to the accompanyingdrawings.

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN). FIG. 1(A) illustrates the structure of aninfrastructure basic service set (BSS) of institute of electrical andelectronic engineers (IEEE) 802.11.

Referring the FIG. 1(A), the WLAN system 10 of the FIG. 1(A) may includeone or more infrastructure BSSs 100 and 105 (hereinafter, referred to asBSS). The BSSs 100 and 105 as a set of an access point (hereinafter,referred to as AP) and a station (hereinafter, referred to STA) such asan AP 110 and a STA1 100-1 which are successfully synchronized tocommunicate with each other are not concepts indicating a specificregion.

For example, the BSS 100 may include one AP 110 and one or more STAs100-1 which may be associated with one AP 110. The BSS 105 may includeone or more STAs 105-1 and 105-2 which may be associated with one AP130.

The infrastructure BSS 100, 105 may include at least one STA, APs 110,130 providing a distribution service, and a distribution system (DS) 120connecting multiple APs.

The distribution system 120 may implement an extended service set (ESS)140 extended by connecting the multiple BSSs 100 and 105. The ESS 140may be used as a term indicating one network configured by connectingone or more APs 110 or 130 through the distribution system 120. The APincluded in one ESS 140 may have the same service set identification(SSID).

A portal 150 may serve as a bridge which connects the WLAN network (IEEE802.11) and another network (e.g., 802.X).

In the BSS illustrated in the FIG. 1(A), a network between the APs 110and 130 and a network between the APs 110 and 130 and the STAs 100-1,105-1, and 105-2 may be implemented.

FIG. 1(B) illustrates a conceptual view illustrating the IBS S.Referring to FIG. 1(B), a WLAN system 15 of FIG. 1(B) may be capable ofperforming communication by configuring a network between STAs in theabsence of the APs 110 and 130 unlike in FIG. 1(A). When communicationis performed by configuring the network also between the STAs in theabsence of the AP 110 and 130, the network is defined as an ad-hocnetwork or an independent basic service set (IBSS).

Referring to the FIG. 1(B), the IBSS is a BSS that operates in an Ad-Hocmode. Since the IBSS does not include the access point (AP), acentralized management entity that performs a management function at thecenter does not exist. That is, in the IBSS 15, STAs 150-1, 150-2,150-3, 155-4, and 155-5 are managed by a distributed manner. In theIBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may be constitutedas movable STAs and are not permitted to access the DS to constitute aself-contained network.

The STA as a predetermined functional medium that includes a mediumaccess control (MAC) that follows a regulation of an Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard and aphysical layer interface for a radio medium may be used as a meaningincluding all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, awireless device, a wireless transmit/receive unit (WTRU), user equipment(UE), a mobile station (MS), a mobile subscriber unit, or just a user.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

As illustrated in FIG. 2, various types of PHY protocol data units(PPDUs) may be used in a standard such as IEEE a/g/n/ac, etc. In detail,LTF and STF fields include a training signal, SIG-A and SIG-B includecontrol information for a receiving station, and a data field includesuser data corresponding to a PSDU.

In the embodiment, an improved technique is provided, which isassociated with a signal (alternatively, a control information field)used for the data field of the PPDU. The signal provided in theembodiment may be applied onto high efficiency PPDU (HE PPDU) accordingto an IEEE 802.11ax standard. That is, the signal improved in theembodiment may be HE-SIG-A and/or HE-SIG-B included in the HE PPDU. TheHE-SIG-A and the HE-SIG-B may be represented even as the SIG-A andSIG-B, respectively. However, the improved signal proposed in theembodiment is not particularly limited to an HE-SIG-A and/or HE-SIG-Bstandard and may be applied to control/data fields having various names,which include the control information in a wireless communication systemtransferring the user data.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

The control information field provided in the embodiment may be theHE-SIG-B included in the HE PPDU. The HE PPDU according to FIG. 3 is oneexample of the PPDU for multiple users and only the PPDU for themultiple users may include the HE-SIG-B and the corresponding HE SIG-Bmay be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) mayinclude a legacy-short training field (L-STF), a legacy-long trainingfield (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A(HE-SIG A), a high efficiency-signal-B (HE-SIG B), a highefficiency-short training field (HE-STF), a high efficiency-longtraining field (HE-LTF), a data field (alternatively, an MAC payload),and a packet extension (PE) field. The respective fields may betransmitted during an illustrated time period (that is, 4 or 8 μs). Moredetailed description of the respective fields of FIG. 3 will be madebelow.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) usedin a band of 20 MHz. As illustrated in FIG. 4, resource units (RUs)corresponding to tone (that is, subcarriers) of different numbers areused to constitute some fields of the HE-PPDU. For example, theresources may be allocated by the unit of the RU illustrated for theHE-STF, the HE-LTF, and the data field.

As illustrated in an uppermost part of FIG. 4, 26 units (that is, unitscorresponding to 26 tones). 6 tones may be used as a guard band in aleftmost band of the 20 MHz band and 5 tones may be used as the guardband in a rightmost band of the 20 MHz band. Further, 7 DC tones may beinserted into a center band, that is, a DC band and a 26-unitcorresponding to each 13 tones may be present at left and right sides ofthe DC band. The 26-unit, a 52-unit, and a 106-unit may be allocated toother bands. Each unit may be allocated for a receiving station, thatis, a user.

Meanwhile, the RU layout of FIG. 4 may be used even in a situation for asingle user (SU) in addition to the multiple users (MUs) and in thiscase, as illustrated in a lowermost part of FIG. 4, one 242-unit may beused and in this case, three DC tones may be inserted.

In one example of FIG. 4, RUs having various sizes, that is, a 26-RU, a52-RU, a 106-RU, a 242-RU, and the like are proposed, and as a result,since detailed sizes of the RUs may extend or increase, the embodimentis not limited to a detailed size (that is, the number of correspondingtones) of each RU.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of FIG. 4, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the likemay be used even in one example of FIG. 5. Further, 5 DC tones may beinserted into a center frequency, 12 tones may be used as the guard bandin the leftmost band of the 40 MHz band and 11 tones may be used as theguard band in the rightmost band of the 40 MHz band.

In addition, as illustrated in FIG. 5, when the RU layout is used forthe single user, the 484-RU may be used. That is, the detailed number ofRUs may be modified similarly to one example of FIG. 4.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of each of FIG. 4 or 5, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU,and the like may be used even in one example of FIG. 6. Further, 7 DCtones may be inserted into the center frequency, 12 tones may be used asthe guard band in the leftmost band of the 80 MHz band and 11 tones maybe used as the guard band in the rightmost band of the 80 MHz band. Inaddition, the 26-RU may be used, which uses 13 tones positioned at eachof left and right sides of the DC band.

Moreover, as illustrated in FIG. 6, when the RU layout is used for thesingle user, 996-RU may be used and in this case, 5 DC tones may beinserted. Meanwhile, the detailed number of RUs may be modifiedsimilarly to one example of each of FIG. 4 or 5.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

A block illustrated in FIG. 7 is another example of describing theHE-PPDU block of FIG. 3 in terms of a frequency.

An illustrated L-STF 700 may include a short training orthogonalfrequency division multiplexing (OFDM) symbol. The L-STF 700 may be usedfor frame detection, automatic gain control (AGC), diversity detection,and coarse frequency/time synchronization. An L-LTF 710 may include along training orthogonal frequency division multiplexing (OFDM) symbol.The L-LTF 710 may be used for fine frequency/time synchronization andchannel prediction.

An L-SIG 720 may be used for transmitting control information. The L-SIG720 may include information regarding a data rate and a data length.Further, the L-SIG 720 may be repeatedly transmitted. That is, a newformat, in which the L-SIG 720 is repeated (e.g., may be referred to asR-LSIG) may be configured.

An HE-SIG-A 730 may include the control information common to thereceiving station.

In detail, the HE-SIG-A 730 may include information on 1) a DL/ULindicator, 2) a BSS color field indicating an identify of a BSS, 3) afield indicating a remaining time of a current TXOP period, 4) abandwidth field indicating at least one of 20, 40, 80, 160 and 80+80MHz, 5) a field indicating an MCS technique applied to the HE-SIG-B, 6)an indication field regarding whether the HE-SIG-B is modulated by adual subcarrier modulation technique for MCS, 7) a field indicating thenumber of symbols used for the HE-SIG-B, 8) a field indicating whetherthe HE-SIG-B is configured for a full bandwidth MIMO transmission, 9) afield indicating the number of symbols of the HE-LTF, 10) a fieldindicating the length of the HE-LTF and a CP length, 11) a fieldindicating whether an OFDM symbol is present for LDPC coding, 12) afield indicating control information regarding packet extension (PE),13) a field indicating information on a CRC field of the HE-SIG-A, andthe like. A detailed field of the HE-SIG-A may be added or partiallyomitted. Further, some fields of the HE-SIG-A may be partially added oromitted in other environments other than a multi-user (MU) environment

An HE-SIG-B 740 may be included only in the case of the PPDU for themultiple users (MUs) as described above. Principally, an HE-SIG-A 750 oran HE-SIG-B 760 may include resource allocation information(alternatively, virtual resource allocation information) for at leastone receiving STA. The HE-SIG-B 740 will be described below in a greaterdetail with reference to FIG. 8.

A previous field of the HE-SIG-B 740 may be transmitted in a duplicatedform on an MU PPDU. In the case of the HE-SIG-B 740, the HE-SIG-B 740transmitted in some frequency band (e.g., a fourth frequency band) mayeven include control information for a data field corresponding to acorresponding frequency band (that is, the fourth frequency band) and adata field of another frequency band (e.g., a second frequency band)other than the corresponding frequency band. Further, a format may beprovided, in which the HE-SIG-B 740 in a specific frequency band (e.g.,the second frequency band) is duplicated with the HE-SIG-B 740 ofanother frequency band (e.g., the fourth frequency band). Alternatively,the HE-SIG B 740 may be transmitted in an encoded form on alltransmission resources. A field after the HE-SIG B 740 may includeindividual information for respective receiving STAs receiving the PPDU.

The HE-STF 750 may be used for improving automatic gain controlestimation in a multiple input multiple output (MIMO) environment or anOFDMA environment.

The HE-LTF 760 may be used for estimating a channel in the MIMOenvironment or the OFDMA environment.

The size of fast Fourier transform (FFT)/inverse fast Fourier transform(IFFT) applied to the HE-STF 750 and the field after the HE-STF 750, andthe size of the FFT/IFFT applied to the field before the HE-STF 750 maybe different from each other. For example, the size of the FFT/IFFTapplied to the HE-STF 750 and the field after the HE-STF 750 may be fourtimes larger than the size of the FFT/IFFT applied to the field beforethe HE-STF 750.

For example, when at least one field of the L-STF 700, the L-LTF 710,the L-SIG 720, the HE-SIG-A 730, and the HE-SIG-B 740 on the PPDU ofFIG. 7 is referred to as a first field, at least one of the data field770, the HE-STF 750, and the HE-LTF 760 may be referred to as a secondfield. The first field may include a field associated with a legacysystem and the second field may include a field associated with an HEsystem. In this case, the fast Fourier transform (FFT) size and theinverse fast Fourier transform (IFFT) size may be defined as a sizewhich is N (N is a natural number, e.g., N=1, 2, and 4) times largerthan the FFT/IFFT size used in the legacy WLAN system. That is, theFFT/IFFT having the size may be applied, which is N (=4) times largerthan the first field of the HE PPDU. For example, 256 FFT/IFFT may beapplied to a bandwidth of 20 MHz, 512 FFT/IFFT may be applied to abandwidth of 40 MHz, 1024 FFT/IFFT may be applied to a bandwidth of 80MHz, and 2048 FFT/IFFT may be applied to a bandwidth of continuous 160MHz or discontinuous 160 MHz.

In other words, a subcarrier space/subcarrier spacing may have a sizewhich is 1/N times (N is the natural number, e.g., N=4, the subcarrierspacing is set to 78.125 kHz) the subcarrier space used in the legacyWLAN system. That is, subcarrier spacing having a size of 312.5 kHz,which is legacy subcarrier spacing may be applied to the first field ofthe HE PPDU and a subcarrier space having a size of 78.125 kHz may beapplied to the second field of the HE PPDU.

Alternatively, an IDFT/DFT period applied to each symbol of the firstfield may be expressed to be N (=4) times shorter than the IDFT/DFTperiod applied to each data symbol of the second field. That is, theIDFT/DFT length applied to each symbol of the first field of the HE PPDUmay be expressed as 3.2 μs and the IDFT/DFT length applied to eachsymbol of the second field of the HE PPDU may be expressed as 3.2 μs*4(=12.8 μs). The length of the OFDM symbol may be a value acquired byadding the length of a guard interval (GI) to the IDFT/DFT length. Thelength of the GI may have various values such as 0.4 μs, 0.8 μs, 1.6 μs,2.4 μs, and 3.2 μs.

For simplicity in the description, in FIG. 7, it is expressed that afrequency band used by the first field and a frequency band used by thesecond field accurately coincide with each other, but both frequencybands may not completely coincide with each other, in actual. Forexample, a primary band of the first field (L-STF, L-LTF, L-SIG,HE-SIG-A, and HE-SIG-B) corresponding to the first frequency band may bethe same as the most portions of a frequency band of the second field(HE-STF, HE-LTF, and Data), but boundary surfaces of the respectivefrequency bands may not coincide with each other. As illustrated inFIGS. 4 to 6, since multiple null subcarriers, DC tones, guard tones,and the like are inserted during arranging the RUs, it may be difficultto accurately adjust the boundary surfaces.

The user (e.g., a receiving station) may receive the HE-SIG-A 730 andmay be instructed to receive the downlink PPDU based on the HE-SIG-A730. In this case, the STA may perform decoding based on the FFT sizechanged from the HE-STF 750 and the field after the HE-STF 750. On thecontrary, when the STA may not be instructed to receive the downlinkPPDU based on the HE-SIG-A 730, the STA may stop the decoding andconfigure a network allocation vector (NAV). A cyclic prefix (CP) of theHE-STF 750 may have a larger size than the CP of another field and theduring the CP period, the STA may perform the decoding for the downlinkPPDU by changing the FFT size.

Hereinafter, in the embodiment of the present invention, data(alternatively, or a frame) which the AP transmits to the STA may beexpressed as a term called downlink data (alternatively, a downlinkframe), and data (alternatively, a frame) which the STA transmits to theAP may be expressed as a term called uplink data (alternatively, anuplink frame). Further, transmission from the AP to the STA may beexpressed as downlink transmission and transmission from the STA to theAP may be expressed as a term called uplink transmission.

In addition, a PHY protocol data unit (PPDU), a frame, and datatransmitted through the downlink transmission may be expressed as termssuch as a downlink PPDU, a downlink frame, and downlink data,respectively. The PPDU may be a data unit including a PPDU header and aphysical layer service data unit (PSDU) (alternatively, a MAC protocoldata unit (MPDU)). The PPDU header may include a PHY header and a PHYpreamble and the PSDU (alternatively, MPDU) may include the frame orindicate the frame (alternatively, an information unit of the MAC layer)or be a data unit indicating the frame. The PHY header may be expressedas a physical layer convergence protocol (PLCP) header as another termand the PHY preamble may be expressed as a PLCP preamble as anotherterm.

Further, a PPDU, a frame, and data transmitted through the uplinktransmission may be expressed as terms such as an uplink PPDU, an uplinkframe, and uplink data, respectively. In the WLAN system to which theembodiment of the present description is applied, the whole bandwidthmay be used for downlink transmission to one STA and uplink transmissionto one STA. Further, in the WLAN system to which the embodiment of thepresent description is applied, the AP may perform downlink (DL)multi-user (MU) transmission based on multiple input multiple output (MUMIMO) and the transmission may be expressed as a term called DL MU MIMOtransmission.

In addition, in the WLAN system according to the embodiment, anorthogonal frequency division multiple access (OFDMA) based transmissionmethod is preferably supported for the uplink transmission and/ordownlink transmission. That is, data units (e.g., RUs) corresponding todifferent frequency resources are allocated to the user to performuplink/downlink communication. In detail, in the WLAN system accordingto the embodiment, the AP may perform the DL MU transmission based onthe OFDMA and the transmission may be expressed as a term called DL MUOFDMA transmission. When the DL MU OFDMA transmission is performed, theAP may transmit the downlink data (alternatively, the downlink frame andthe downlink PPDU) to the plurality of respective STAs through theplurality of respective frequency resources on an overlapped timeresource. The plurality of frequency resources may be a plurality ofsubbands (alternatively, sub channels) or a plurality of resource units(RUs). The DL MU OFDMA transmission may be used together with the DL MUMIMO transmission. For example, the DL MU MIMO transmission based on aplurality of space-time streams (alternatively, spatial streams) may beperformed on a specific subband (alternatively, sub channel) allocatedfor the DL MU OFDMA transmission.

Further, in the WLAN system according to the embodiment, uplinkmulti-user (UL MU) transmission in which the plurality of STAs transmitsdata to the AP on the same time resource may be supported. Uplinktransmission on the overlapped time resource by the plurality ofrespective STAs may be performed on a frequency domain or a spatialdomain.

When the uplink transmission by the plurality of respective STAs isperformed on the frequency domain, different frequency resources may beallocated to the plurality of respective STAs as uplink transmissionresources based on the OFDMA. The different frequency resources may bedifferent subbands (alternatively, sub channels) or different resourcesunits (RUs). The plurality of respective STAs may transmit uplink datato the AP through different frequency resources. The transmission methodthrough the different frequency resources may be expressed as a termcalled a UL MU OFDMA transmission method.

When the uplink transmission by the plurality of respective STAs isperformed on the spatial domain, different time-space streams(alternatively, spatial streams) may be allocated to the plurality ofrespective STAs and the plurality of respective STAs may transmit theuplink data to the AP through the different time-space streams. Thetransmission method through the different spatial streams may beexpressed as a term called a UL MU MIMO transmission method.

The UL MU OFDMA transmission and the UL MU MIMO transmission may be usedtogether with each other. For example, the UL MU MIMO transmission basedon the plurality of space-time streams (alternatively, spatial streams)may be performed on a specific subband (alternatively, sub channel)allocated for the UL MU OFDMA transmission.

In the legacy WLAN system which does not support the MU OFDMAtransmission, a multi-channel allocation method is used for allocating awider bandwidth (e.g., a 20 MHz excess bandwidth) to one terminal. Whena channel unit is 20 MHz, multiple channels may include a plurality of20 MHz-channels. In the multi-channel allocation method, a primarychannel rule is used to allocate the wider bandwidth to the terminal.When the primary channel rule is used, there is a limit for allocatingthe wider bandwidth to the terminal. In detail, according to the primarychannel rule, when a secondary channel adjacent to a primary channel isused in an overlapped BSS (OBSS) and is thus busy, the STA may useremaining channels other than the primary channel. Therefore, since theSTA may transmit the frame only to the primary channel, the STA receivesa limit for transmission of the frame through the multiple channels.That is, in the legacy WLAN system, the primary channel rule used forallocating the multiple channels may be a large limit in obtaining ahigh throughput by operating the wider bandwidth in a current WLANenvironment in which the OBSS is not small.

In order to solve the problem, in the embodiment, a WLAN system isdisclosed, which supports the OFDMA technology. That is, the OFDMAtechnique may be applied to at least one of downlink and uplink.Further, the MU-MIMO technique may be additionally applied to at leastone of downlink and uplink. When the OFDMA technique is used, themultiple channels may be simultaneously used by not one terminal butmultiple terminals without the limit by the primary channel rule.Therefore, the wider bandwidth may be operated to improve efficiency ofoperating a wireless resource.

As described above, in case the uplink transmission performed by each ofthe multiple STAs (e.g., non-AP STAs) is performed within the frequencydomain, the AP may allocate different frequency resources respective toeach of the multiple STAs as uplink transmission resources based onOFDMA. Additionally, as described above, the frequency resources eachbeing different from one another may correspond to different subbands(or sub-channels) or different resource units (RUs).

The different frequency resources respective to each of the multipleSTAs are indicated through a trigger frame.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

As illustrated in FIG. 8, the HE-SIG-B field includes a common field ata frontmost part and the corresponding common field is separated from afield which follows therebehind to be encoded. That is, as illustratedin FIG. 8, the HE-SIG-B field may include a common field including thecommon control information and a user-specific field includinguser-specific control information. In this case, the common field mayinclude a CRC field corresponding to the common field, and the like andmay be coded to be one BCC block. The user-specific field subsequentthereafter may be coded to be one BCC block including the “user-specificfield” for 2 users and a CRC field corresponding thereto as illustratedin FIG. 8.

FIG. 9 illustrates an example of a trigger frame. The trigger frame ofFIG. 9 allocates resources for Uplink Multiple-User (MU) transmissionand may be transmitted from the AP. The trigger frame may be configuredas a MAC frame and may be included in the PPDU. For example, the triggerframe may be transmitted through the PPDU shown in FIG. 3, through thelegacy PPDU shown in FIG. 2, or through a certain PPDU, which is newlydesigned for the corresponding trigger frame. In case the trigger frameis transmitted through the PPDU of FIG. 3, the trigger frame may beincluded in the data field shown in the drawing.

Each of the fields shown in FIG. 9 may be partially omitted, or otherfields may be added. Moreover, the length of each field may be varieddifferently as shown in the drawing.

A Frame Control field 910 shown in FIG. 9 may include informationrelated to a version of the MAC protocol and other additional controlinformation, and a Duration field 920 may include time information forconfiguring a NAV or information related to an identifier (e.g., AID) ofthe user equipment.

In addition, the RA field 930 may include address information of thereceiving STA of a corresponding trigger frame, and may be optionallyomitted. The TA field 940 includes address information of an STA (e.g.,AP) for transmitting the trigger frame, and the common information field950 includes common control information applied to the receiving STA forreceiving the trigger frame.

It is preferable that the trigger frame of FIG. 9 includes per userinformation fields 960#1 to 960# N corresponding to the number ofreceiving STAs receiving the trigger frame of FIG. 9. The per userinformation field may also be referred to as a “RU Allocation field”.Additionally, the trigger frame of FIG. 9 may include a Padding field970 and a Sequence field 980.

It is preferable that each of the per user information fields 960#1 to960# N shown in FIG. 9 further includes multiple sub-fields.

FIG. 10 illustrates an example of a sub-field included in a per userinformation field. Some parts of the sub-field of FIG. 10 may beomitted, and extra sub-fields may be added. Further, a length of each ofthe sub-fields shown herein may change.

As shown in the drawing, the Length field 1010 may be given that samevalue as the Length field of the L-SIG field of the uplink PPDU, whichis transmitted in response to the corresponding trigger frame, and theLength field of the L-SIG field of the uplink PPDU indicates the lengthof the uplink PPDU. As a result, the Length field 1010 of the triggerframe may be used for indicating the length of its respective uplinkPPDU.

Additionally, a Cascade Indicator field 1020 indicates whether or not acascade operation is performed. The cascade operation refers to adownlink MU transmission and an uplink MU transmission being performedsimultaneously within the same TXOP. More specifically, this refers to acase when a downlink MU transmission is first performed, and, then,after a predetermined period of time (e.g., SIFS), an uplink MUtransmission is performed. During the cascade operation, only onetransmitting device performing downlink communication (e.g., AP) mayexist, and multiple transmitting devices performing uplink communication(e.g., non-AP) may exist.

A CS Request field 1030 indicates whether or not the status or NAV of awireless medium is required to be considered in a situation where areceiving device that has received the corresponding trigger frametransmits the respective uplink PPDU.

A HE-SIG-A information field 1040 may include information controllingthe content of a SIG-A field (i.e., HE-SIG-A field) of an uplink PPDU,which is being transmitted in response to the corresponding triggerframe.

A CP and LTF type field 1050 may include information on a LTF length anda CP length of the uplink PPDU being transmitted in response to thecorresponding trigger frame. A trigger type field 1060 may indicate apurpose for which the corresponding trigger frame is being used, e.g.,general triggering, triggering for beamforming, and so on, a request fora Block ACK/NACK, and so on.

In the present specification, it may be assumed that a Trigger Typefield 1060 of the trigger frame indicates a trigger frame of a basictype for general triggering. For example, a trigger frame of a basictype may be referred to as a basic trigger frame.

FIG. 11 illustrates an example of a sub-field being included in a peruser information field.

The per user information field 1100 of FIG. 11 may be construed as oneof the individual user information fields 960#1 to 960# N illustrated inFIG. 9.

Among the sub-fields of FIG. 11, some may be omitted, and otheradditional sub-fields may also be added. Additionally, the length ofeach of the sub-fields shown in the drawing may be varied.

A User Identifier field 1110 indicates an identifier of an STA (i.e.,receiving STA) to which the per user information corresponds, and anexample of the identifier may correspond to all or part of anassociation identifier AID.

Additionally, a RU Allocation field 1120 may be included in thesub-field of the per user information field. More specifically, in casea receiving STA, which is identified by the User Identifier field 1110,transmits an uplink PPDU in response to the trigger frame of FIG. 9, thecorresponding uplink PPDU is transmitted through the RU, which isindicated by the RU Allocation field 1120. In this case, it ispreferable that the RU that is being indicated by the RU Allocationfield 1120 corresponds to the RU shown in FIG. 4, FIG. 5, and FIG. 6.

The sub-field of FIG. 11 may include a Coding Type field 1130. TheCoding Type field 1130 may indicate a coding type of the uplink PPDUbeing transmitted in response to the trigger frame of FIG. 9. Forexample, in case BBC coding is applied to the uplink PPDU, the CodingType field 1130 may be set to ‘1’, and, in case LDPC coding is appliedto the uplink PPDU, the Coding Type field 1130 may be set to ‘0’.

Additionally, the sub-field of FIG. 11 may include a MCS field 1140. TheMCS field 1140 may indicate a MCS scheme being applied to the uplinkPPDU that is transmitted in response to the trigger frame of FIG. 9.

For example, when BCC coding may is applied to the uplink PPDU, thecoding type field 1130 may be set to ‘1’, and when the LDPC coding isapplied, the coding type field 1130 may be set to ‘0’.

In the present specification, a basic trigger frame may be construed asa variant of a trigger frame. A basic trigger frame may further includea trigger dependent user information field 1150 in each individual userinformation field 960#1 to 960# N.

The Trigger dependent User Info field 1150 will be described in moredetail later on with reference to FIG. 18.

FIG. 12 is a diagram illustrating an EDCA-based channel access method ina WLAN system. In a WLAN system, an STA (or AP) may perform channelaccess in accordance with a plurality of user priority levels that aredefined for enhanced distributed channel access (EDCA).

More specifically, in order to transmit a quality of service (QoS) dataframe that is based on the plurality of user priority levels, fouraccess categories (ACs) (i.e., background (AC_BK), best effort (AC_BE),video (AC_VI), and voice (AC_VO)) may be defined.

The STA may receive traffic data (e.g., a MAC service data unit (MSDU))having a predetermined user priority level from a higher layer (e.g., alogical link control (LLC) layer).

For example, in order to determine the transmission order of the MACframe that is to be transmitted by the STA, a differential value may beconfigured for each set of traffic data in the user priority level. Theuser priority level may be mapped to each access category (AC), whereinthe traffic data are buffered, by using the method shown in Table 1.

TABLE 1 Priority level User priority level Access Category (AC) Low 1AC_BK 2 AC_BK 0 AC_BE 3 AC_BE 4 AC_VI 5 AC_VI 6 AC_VO High 7 AC_VO

In this specification, the user priority level may be construed as aTraffic identifier (hereinafter referred to as ‘TID’) indicating thecharacteristics of traffic data.

Referring to Table 1, traffic data having a user priority level (i.e.,TID) of ‘1’ or ‘2’ may be buffered to a transmission queue 1250 of theAC_BK type. Traffic data having a user priority level (i.e., TID) of ‘0’or ‘3’ may be buffered to a transmission queue 1240 of the AC_BE type.

Traffic data having a user priority level (i.e., TID) of ‘4’ or ‘5’ maybe buffered to a transmission queue 1230 of the AC_VI type. And, trafficdata having a user priority level (i.e., TID) of ‘6’ or ‘7’ may bebuffered to a transmission queue 1220 of the AC_VO type. Instead of DCFinterframe space (DIFS), CWmin, and CWmax, which correspond toparameters for a backoff procedure that is based on the legacydistributed coordination function (DCF), a set (or group) of EDCAparameters, which corresponds to arbitration interframe space(AIFS)[AC], CWmin[AC], CWmax[AC], and TXOP limit[AC] may be used.

A difference in transmission priority levels may be implemented based ona set of differential EDCA parameters. An example of default values ofthe set of EDCA parameters (i.e., AIFS[AC], CWmin[AC], CWmax[AC], TXOPlimit[AC]) corresponding to each AC may be as shown below in Table 2.

TABLE 2 AC CWmin[AC] CWmax[AC] AIFS[AC] TXOP limit[AC] AC_BK 31 1023 7 0AC_BE 31 1023 3 0 AC_VI 15 31 2 3.008 ms AC_VO 7 15 2 1.504 ms

The set of EDCA parameters for each AC may be configured to have defaultvalues or may be loaded in beacon frame so as to be transmitted from anAP to each STA. As values of AIFS[AC] and CWmin[AC] become smaller, thecorresponding priority level may become higher, and, accordingly,channel access delay may become shorter, thereby enabling a largernumber of bands to be used in the given traffic environment.

The set of EDCA parameters may include information on the channel accessparameters (e.g., AIFS [AC], CWmin[AC], CWmax[AC]) for each AC.

The backoff procedure for EDCA may be performed based on a set of EDCAparameters, each being individually configured for 4 ACs included ineach STA. An adequate configuration of EDCA parameter values definingdifferent channel access parameters for each AC may optimize networkperformance and may, at the same time, increase the transmission effect,which results from the priority level of the traffic.

Therefore, in order to ensure equal (or fair) media access for all STAsparticipating in the network, the AP of the WLAN system should becapable of performing overall management and coordination functionscorresponding to the EDCA parameters.

Referring to FIG. 12, one STA (or AP) 1200 may include a virtual mapper1210, a plurality of transmission queues 1220 to 1250, and a virtualcollision handler 1260. The virtual mapper 1210 of FIG. 12 may perform afunction of mapping an MSDU that is received from a logical link control(LLC) layer to transmission queues corresponding to each AC inaccordance with the Table 1, which is presented above.

The plurality of transmission queues 1220 to 1250 may perform thefunctions of individual EDCA contention entities for wireless mediaaccess within an STA (or AP). For example, the transmission queue 1220of the AC_VO type of FIG. 12 may include one frame 1221 for a second STA(not shown).

The transmission queue 1230 of the AC_VI type may include 3 frames 1231to 1233 for a first STA (not shown) and one frame 1234 for a third STAin accordance with a transmission order by which the frames are to betransmitted to a physical layer.

The transmission queue 1240 of the AC_BE type of FIG. 12 may include oneframe 1241 for a second STA (not shown), and one frame 1242 for a thirdSTA (not shown) and one frame 1243 for a second STA (not shown) inaccordance with a transmission order by which the frames are to betransmitted to a physical layer.

As an example, the transmission queue 1250 of the AC_BK type of FIG. 12may not include a frame that is to be transmitted to a physical layer.

For example, the frame 1221 included in the transmission queue 1220 ofthe AC_VO type of FIG. 12 may be interpreted and understood as one MACProtocol Data Unit (MPDU) that is concatenated with a plurality oftraffic data (i.e., MSDUs), which are received from a higher layer(i.e., LLC layer).

Also, the frame 1221 included in the transmission queue 1220 of theAC_VO type of FIG. 12 may be interpreted and understood as one MPDU thatis concatenated with a plurality of traffic data (i.e., MSDUs) havingthe traffic identifier (TID) of any one of ‘6’ and ‘7’.

The frame 1231 included in the transmission queue 1230 of the AC_VI typeof FIG. 12 may be interpreted and understood as one MAC Protocol DataUnit (MPDU) that is concatenated with a plurality of traffic data (i.e.,MSDUs), which are received from a higher layer (i.e., LLC layer).

Also, the frame 1231 included in the transmission queue 1230 of theAC_VI type of FIG. 12 may be interpreted and understood as one MPDU thatis concatenated with a plurality of traffic data (i.e., MSDUs) havingthe traffic identifier (TID) of any one of ‘4’ and ‘5’.

Similarly, each of the other frames 1232, 1233, and 1234 included in thetransmission queue 1230 of the AC_VI type may be interpreted andunderstood as one MPDU that is concatenated with a plurality of trafficdata (i.e., MSDUs) having the traffic identifier (TID) of any one of ‘4’and ‘5’.

Furthermore, the frame 1241 included in the transmission queue 1240 ofthe AC_BE type may be interpreted and understood as one MPDU that isconcatenated with a plurality of traffic data (i.e., MSDUs) having thetraffic identifier (TID) of any one of ‘0’ and ‘3’. Similarly, each ofthe other frames 1242 and 1243 included in the transmission queue 1240of the AC_BE type may be interpreted and understood as one MPDU that isconcatenated with a plurality of traffic data (i.e., MSDUs) having thetraffic identifier (TID) of any one of ‘0’ and ‘3’.

Each of the frames 1221, 1231 to 1234, and 1241 to 1243 may beinterpreted and understood as a frame that does not exceed apredetermined traffic size.

In case one or more ACs having completed the backoff at the same timeexist(s), the collision between the ACs may be coordinated in accordancewith an EDCA function (EFCAF) included in the virtual collision handler1260.

More specifically, by transmitting the frame included in the AC havingthe higher priority level, among the ACs that collide with one another,the problem of collision within the STA may be resolved. In this case,another AC may increase its contention window, and, then, the other ACmay update its backoff counter with a newly selected backoff value basedon the increased contention window.

A transmission opportunity (TXOP) may be initiated when a channel isaccessed in accordance with an EDCA rule. When two or more frames areaccumulated in one AC, and if an EPCA TXOP is acquired, the AC of anEDCA MAC layer may attempt to perform multiple frame transmissions. Ifthe STA has already transmitted one frame, and if the STA is alsocapable of receiving the transmission of a next frame existing in thesame AC within the remaining TXOP time and along with its ACK, the STAmay attempt to perform the transmission of the corresponding frame afteran SIFS time interval.

A TXOP limit value may be configured as a default value in the AP andthe STA, and a frame that is related to the TXOP limit value may betransported (or delivered) to the STA from the AP.

If the size of the data frame that is to be transmitted exceeds the TXOPlimit value, the AP may perform fragmentation on the corresponding frameinto a plurality of smaller frames. Subsequently, the fragmented framesmay be transmitted within a range that does not exceed the TXOP limitvalue.

FIG. 13 is a conceptual view illustrating a backoff procedure of anEDCA.

A plurality of STAs may share a wireless medium based on a distributedcoordination function (hereinafter referred to as ‘DCF’). In order tocontrol the collision between STAs, the DCF may use a carrier sensemultiple access/collision avoidance (hereinafter referred to as CSMA/CA)as its access protocol.

In a channel access method using the DCF, if a medium is not used duringone DCF inter frame space (DIFS) (i.e., if the channel is idle) the STAmay transmit an MPDU that is internally determined.

When it is determined by the carrier sensing mechanism that the wirelessmedium is used by another STA (i.e., that the channel is busy), the STAmay determine the size of the contention window (hereinafter referred toas ‘CW’) and may then perform a backoff procedure.

In order to perform the backoff procedure, each STA may configure abackoff value, which is arbitrarily selected within the contentionwindow (CW), in the backoff counter. In this specification, the timeindicating the backoff value, which is selected by each STA, may beinterpreted and understood as the backoff window shown in FIG. 13.

By counting down the backoff window in slot time units, each STA mayperform a backoff procedure for channel access. Among the plurality ofSTAs, an STA that has selected the relatively shortest backoff windowmay acquire a transmission opportunity (hereinafter referred to as‘TXOP’), which corresponds to an authority to occupy a medium.

During a time period (or time section) for the TXOP, the remaining STAsmay suspend their countdown operations. The remaining STAs may go onstandby (or enter a standby mode) until the time period for the TXOP isended. After the time period for the TXOP is ended, the remaining STAsmay resume their countdown operations, which were suspended earlier.

By using the transmission method that is based on such DCF, the problemof collision, which may occur when a plurality of STAs transmit framessimultaneously, may be prevented. However, the channel access methodusing DCF does not have the concept of transmission priority levels(i.e., user priority levels). More specifically, when using the DCF, thequality of service (QoS) of the traffic that is intended to betransmitted by the STA cannot be ensured.

In order to resolve this problem, a hybrid coordination function(hereinafter referred to as ‘HCF’), which is new coordination function,has been defined in 802.11e. The newly defined HCF has a capability (orperformance) that is more enhanced than the channel access performance(or capability) of the legacy DCF. For the purposed of enhancing theQoS, the HCF may also use two different types of channel access methods,which correspond to a HCF controlled channel access (HCCA) of a pollingmethod and a contention based enhanced distributed channel access(EDCA).

Referring to FIG. 13, the STA assumes that EDCA is being performed forthe transmission of traffic data that are buffered to the STA. Referringto Table 1, the user priority level configured for each set of trafficdata may be differentiated to 8 levels. Each STA may include 4 differenttypes (AC_BK, AC_BE, AC_VI, AC_VO) of output queues being mapped to 8levels of user priority levels shown in Table 1.

The STA according to the exemplary embodiment of the present inventionmay transmit traffic data based on an Arbitration Interframe Space(AIFS) corresponds to the user priority level instead of the DCFInterframe Space (DIFS), which was used in the legacy method.

Hereinafter, in the exemplary embodiment of the present invention, auser equipment may correspond to a device that is capable of supportingboth a WLAN system and a cellular system. More specifically, the userequipment may be interpreted as a UE supporting a cellular system or anSTA supporting a WLAN system.

In order to facilitate the description of this specifically, Inter-FrameSpacing, which is mentioned in 802.11, will be described. For example,Inter-Frame Spacing (IFS) may correspond to a reduced interframe space(RIFS), a short interframe space (SIFS), a PCF interframe space (PIFS),a DCF interframe space (DIFS), an arbitration interframe space (AIFS),or an extended interframe space (EIFS).

The Inter-Frame Spacing (IFS) may be determined in accordance withattributes specified by the physical layer of the STA regardless of thebit rate of the STA. Among the Inter-Frame Spacing (IFS), with theexception for the AIFS, the remaining IFS may be understood as a fixedvalue for each physical layer.

The AIFS may be configured of have a value corresponding to the 4 typesof transmission queues that are mapped to the user priority level, asshown in Table 2.

The SIFS has the shortest time gap among the IFS mentioned above.Accordingly, the SIFS may be used when an STA occupying a wirelessmedium is required to maintain its occupation of the medium without anyinterruption by another STA during a section, wherein a frame exchangesequence is performed.

More specifically, by using the shortest gap between transmissionswithin a frame exchange sequence, priority may be assigned (or given)for completing the frame exchange sequence that is being performed.Also, an STA performing access to a wireless medium by using SIFS mayimmediately initiate transmission from an SIFS boundary withoutdetermining whether or not the medium is busy.

A duration of an SIFS for a specific physical (PHY) layer may be definedby a SIFSTime parameter. For example, in the physical (PHY) layer of theIEEE 802.11a, IEEE 802.11g, IEEE 802.11n, and IEEE 802.11ac standards(or specifications), the SIFS value is equal to 16 μs.

The PIFS may be used in order to provide the STA with a higher prioritylevel following the SIFS. More specifically, the PIFS may be used inorder to acquire a priority for accessing the wireless medium.

The DIFS may be used by an STA transmitting a data frame (MPDU) and amanagement frame (Mac Protocol Data Unit (MPDU)) based on the DCF.

After the received frame and backoff time are expired, when it isdetermined that the medium is in an idle state by a carrier sense (CS)mechanism, the STA may transmit a frame.

FIG. 14 is a diagram describing a transmission procedure of a frame in aWLAN system.

As described above each of the STAs 1410, 1420, 1430, 1440, and 1450according to the exemplary embodiment of the present invention mayindividually select a backoff value of the backoff procedure.

Additionally, each STA 1410, 1420, 1430, 1440, and 1450 may attempt toperform transmission after going on standby for as long as a time period(i.e., backoff window of FIG. 13), which indicates the selected backoffvalue in slot time units.

Moreover, each STA 1410, 1420, 1430, 1440, and 1450 may performcountdown of a backoff window in slot time units. The countdownoperations for channel access corresponding to the wireless medium maybe individually performed by each STA.

Hereinafter, the time corresponding to the backoff window may bereferred to as a random backoff time Tb[i]. In other words, each STA mayindividually configure a backoff time (Tb[i]) in the backoff counter ofeach STA.

More specifically, the backoff time Tb[i] corresponds to a pseudo-randominteger value and may be calculated based on Equation 1 shown below.T _(b)[i]=Random(i)×Slot Time  [Equation 1]

Random(i) of Equation 1 refers to a function using uniform distributionand generating a random integer between 0 and CW[i]. CW[i] may beinterpreted as a contention window that is selected between a minimumcontention window CWmin[i] and a maximum contention window CWmax[i]. Theminimum contention window CWmin[i] and the maximum contention windowCWmax[i] may correspond to CWmin[AC] and CWmax[AC], which representdefault values of Table 2.

In an initial channel access, the STA may set the CW[i] as a CWmin[i]and may select a random integer between 0 and CWmin[i]. In the exemplaryembodiment of the present invention, the selected random integer may bereferred to as a backoff value.

i may be interpreted and understood as a user priority level of thetraffic data. i of Equation 1 may be interpreted and understood tocorrespond to any one of AC_VO, AC_VI, AC_BE, and AC_BK according toTable 1.

The SlotTime of Equation 1 may be used for providing sufficient time inorder to allow the preamble of the transmitting STA to be sufficientlydetected by a neighboring STA. The SlotTime of Equation 1 may be usedfor defining the PIFS and DIFS, which are mentioned above. For example,the SlotTime may be equal to 9 μs.

For example, in case the user priority level (i) is equal to ‘7’, aninitial backoff time for the transmission queue of the AC_VO typeTb[AC_VO] may correspond to a time indicating the backoff time, which isselected between 0 and CWmin[AC_VO], in SlotTime units.

In case collision occurs between STAs in accordance with the backoffprocedure (or in case an ACK frame corresponding to the transmittedframe fails to be received), the STA may calculate the increased backofftime Tb[i]′ based on Equation 2 shown below.CW _(new)[i]=(CW _(old)[i]+1)×PF)−1  [Equation 2]

Referring to Equation 2, a new contention window CW_(new)[i] may becalculated based on a previous (or old) contention window. A PF value ofEquation 2 may be calculated in accordance with a procedure that isdefined in the IEEE 802.11e standard. For example, the PF value ofEquation 2 may be configured to be equal to ‘2’.

In this exemplary embodiment, the increased backoff time Tb[i]′ may beinterpreted and understood as a time indicating a random integer (i.e.,backoff value) that is selected between 0 and the new contention windowCW_(new)[i] in slot time units.

The CWmin[i], CWmax[i], AIFS[i], and PF values, which are mentioned inFIG. 14, may be signaled from the AP through a QoS parameter setelement, which corresponds to a management frame. The values ofCWmin[i], CWmax[i], AIFS[i], and PF may correspond to values that arepredetermined by the AP and the STA.

Referring to FIG. 14, a horizontal axis for first to fifth STAs 1410 to1450 may indicate a time axis. And, a vertical axis for the first tofifth STAs 1410 to 1450 may indicate the backoff time.

Referring to FIG. 13 and FIG. 14, if a state of a specific medium ischanged from an idle state to a busy (or occupied) state, the pluralityof STAs may attempt to perform data (or frame) transmission.

At this point, as a method for minimizing collision between STAs, eachSTA may select a backoff time Tb[i] of Equation 1 and may attempt toperform transmission after going on standby for as long as a slot timecorresponding to the selected backoff time.

In case the backoff procedure is initiated, each STA may performcountdown of a backoff counter time, which is individually selected, inslot time units. Each STA may continuously monitor the medium whileperforming the countdown.

If the wireless medium is monitored while it is in an occupied state,the STA may suspend the countdown and may go on standby (or enter astandby mode). If the wireless medium is monitored while it is in anidle state, the STA may resume countdown.

Referring to FIG. 14, when a frame for the third STA 1430 reaches theMAC layer of the third STA 1430, the third STA 1430 may determinewhether or not the medium is in an idle state during a DIFS.Subsequently, when it is determined that the medium is in the idle stateduring a DIFS, the third STA 1430 may transmit a frame to the AP (notshown). Herein, however, although the inter frame space (IFS) of FIG. 14is illustrated as a DIFS, it should be understood that thisspecification will not be limited only to this.

While the frame is transmitted from the third STA 1430, the remainingSTAs may verify the occupation status of the medium and may then enter astandby mode during the transmission period of the frame. The may reachthe MAC layer corresponding to each of the first STA 1410, the secondSTA 1420, and the fifth STA 1450. If it is determined that the medium isin an idle state, each STA may be on standby for as long as a DIFS andmay then perform countdown of a backoff time, which is individuallyselected by each STA.

FIG. 14 illustrates a case when the second STA 1420 selects the smallest(or shortest) backoff time and when the first STA 1410 selects thelargest (or longest) backoff time. More specifically, FIG. 14illustrates a case when the remaining backoff time of the fifth STA 1450is shorter than the remaining backoff time of the first STA 1410, at atime point T1 of completing the backoff procedure corresponding to thebackoff time, which is selected by the second STA 1420, and initiatingthe frame transmission.

When the medium is occupied by the second STA 1420, the first STA 1410and the fifth STA 1450 may suspend the backoff procedure and go onstandby. Subsequently, when the medium of the second STA 1420 occupationis ended (i.e., when the medium returns to its idle state), the firstSTA 1410 and the fifth STA 1450 may go on standby for as long as a DIFS.

Thereafter, the first STA 1410 and the fifth STA 1450 may resume theirbackoff procedures based on the suspended remaining backoff time. Inthis case, since the remaining backoff time of the fifth STA 1450 isshorter than the remaining backoff time of the first STA 1410, the fifthSTA 1450 may complete the backoff procedure earlier than the first STA1410. Meanwhile, referring to FIG. 14, when the medium is occupied bythe second STA 1420, a frame for the fourth STA 1440 may reach the MAClayer of the fourth STA 1440. When the medium enters (or returns to) theidle state, the fourth STA 1440 may go on standby for as long as a DIFS.Thereafter, the fourth STA 1440 may perform countdown of the backofftime, which is selected by the fourth STA 1440.

Referring to FIG. 14, the remaining backoff time of the fifth STA 1450may coincidently match with (or be identical to) the remaining backofftime of the fourth STA 1440. In this case, collision may occur betweenthe fourth STA 1440 and the fifth STA 1450. If collision occurs betweenthe STAs, both the fourth STA 1440 and the fifth STA 1450 may becomeincapable of receiving ACKs and may fail to perform data transmission.

Accordingly, the fourth STA 1440 and the fifth STA 1450 may individuallycalculate a new contention window CW_(new)[i] in accordance withEquation 2, which is presented above. Subsequently, the fourth STA 1440and the fifth STA 1450 may individually perform countdown of the backofftime, which is newly calculated in accordance with Equation 2.Meanwhile, when then medium is in an occupied state due to thetransmission of the fourth STA 1440 and the fifth STA 1450, the firstSTA 1410 may go on standby. Subsequently, if the medium enters (orreturns to) the idle state, after being on standby for as long as a DIFSand may then resume the backoff counting. When the backoff time of thefirst STA 1410 is elapsed, the first STA 1410 may transmit a frame.

In addition to physical carrier sensing by which the AP and/or STAdirectly senses the medium, the CSMA/CA mechanism may also includevirtual carrier sensing.

Virtual carrier sensing is used for compensating for any problems thatmay occur during access to the medium, such as a hidden node problem,and so on. For the virtual carrier sensing, the MAC of a WLAN systemuses a Network Allocation Vector (NAV). Herein, the NAV corresponds to avalue, which corresponds to the time remaining until the medium shiftsto an available state, that is indicated by an AP and/or STA currentlyusing or having the authority to use the medium to another AP and/orSTA.

Therefore, the value that is configured as the NAV corresponds to a timeperiod during which the usage of the medium by the AP and/or STAtransmitting corresponding frame is scheduled, and, during thecorresponding time period, medium access of the STA receiving the NAVvalue is prohibited.

FIG. 15 illustrates an example of a MAC frame. In this specification, aMAC frame 1500 of FIG. 15 may be interpreted and understood as one MPDU.

Referring to FIG. 15, the MAC frame 1500 may include a plurality offields 1511 to 1519 for the MAC header, a frame body field 1520including a payload, and a FCS field 1530 for error detection of areceiving device. For example, the frame body field 1520 may have avariable length.

Among the plurality of fields 1511 to 1519 included in the MAC header, aframe control field 1511, a duration/ID field 1512, and a first addressfield 1513, and the FCS field 1530 may be included in all types of MACframes.

A second address field 1514, a third address field 1515, a sequencecontrol field 1516, a fourth address field 1517, a QoS control field1518, a HT control field 1519, and a frame body field 1520 may beselectively included in accordance with the type of the MAC frame.

When a QoS data frame or a QoS null frame is indicated through the framecontrol field 1511, the QoS control field 1518 may be included in theMAC frame 1500.

In this specification, the QoS data frame may refer to a frame includinga payload (e.g., MSDU) included in the frame body field 1520.Additionally, the QoS null frame does not include a payload in the framebody field 1520 and may refer to a frame including control informationin the MAC header 1511 to 1519.

The QoS control field 1518 may be configured of 2 octets (16 bits). TheQoS control field 1518 may configured as shown below in Table 3.

TABLE 3 Applicable frame (sub) types Bits 0-3 Bit 4 Bits 5-6 Bit 7 Bits8 Bit 9 Bit 10 Bits 11-15 QoS Data and QoS Data + TID 0 Ack A-MSDU TXOPDuration Requested CF-Ack frames sent by Policy Present non-AP STAs thatare not TID 1 Ack A-MSDU Queue Size a TPU butter STA or a TPU PolicyPresent sleep STA in nonmesh BSS QoS Null frames sent by TID 0 AckReserved TXOP Duration Requested non-AP STAs that are not Policy a TPUbutter STA or a TPU TID 1 Ack Reserved Queue Size sleep STA in nonmeshBSS Policy

Referring to Table 3, first to fourth bits Bit0 to Bit3 may correspondto a region for a traffic identifier (hereinafter referred to as ‘TID’).The traffic identifier (TID) may be mapped to ‘0’ to ‘7’ for the userpriority levels shown in Table 1. The remaining values 8 to 15, whichare expressed by the first to fourth bits Bit0 to Bit3, may correspondto reserved values.

The traffic identifier (TID), which corresponds to the traffic beingbuffered to the STA (or AP) may be delivered (or transported) throughthe first bit to the fourth bit Bit0 to Bit3 of the QoS control field1518.

For example, if the fifth bit Bit4 of the QoS control field 1518 is setto ‘1’, queue size information of the transmission queue correspondingto the traffic that is to be transmitted by the STA may be included inthe ninth bit to sixteenth bit Bit8 to Bit15 of the QoS control field1518.

Referring to FIG. 12 to FIG. 15, in case the traffic identifier (TID) ofthe buffered traffic 1221 is set to ‘6’ or ‘7’, the STA 1200 mayindicate a queue size of the traffic 1221, which is buffered to thetransmission 1220 of the AC_VO type, through the QoS control field 1518of the MAC frame 1500.

As another example, in case the traffic identifier (TID) of the bufferedtraffic 1221 is set to ‘4’ or ‘5’, the STA 1200 may indicate a summed(or combined) queue size of the traffic 1231 to 1234 being buffered tothe transmission queue 1230 of the AC_VI type.

FIG. 16 is a conceptual view illustrating a frame structure of an MPDUthat is generated based on a plurality of MSDUs according to anembodiment.

Referring to FIG. 1 to FIG. 16, the MPDU 1600 may correspond to the MACframe 150 of FIG. 15. For example, the MPDU 1600 of the MAC header 1601may correspond to the MAC header 1511 to 1519 of FIG. 15. A frame bodyfield 1602 of the MPDU 1600 may correspond to the frame body field 1520of FIG. 15. A FCS field 1603 of the MPDU 1600 may correspond to the FCSfield 1530 of FIG. 15.

More specifically, a frame having two encapsulated MSDUs 1610 and 1620aggregated therein may be included in the frame body field 1602 of FIG.16.

For example, the first encapsulated MSDU 1610 may be generated based ona first payload (i.e., MSDU #1) that is received by the MAC layer froman LLC layer, which is a higher layer. For example, the firstencapsulated MSDU 1610 may include a first subframe header having apredetermined size.

The first subframe header may include a first destination addressDestination Address #1 (hereinafter referred to as ‘DA #1’), a firstsource address Source Address #1 (hereinafter referred to as ‘SA #1’),and a first length field (hereinafter referred to as ‘L #1’), whichindicates information on the length of a payload (i.e., MSDU #1).

Also, the first encapsulated MSDU 1610 may include a pad field having apredetermined size. The first encapsulated PSDU 1610 and the secondencapsulated MSDU 1620 may be logically (or physically) differentiatedfrom one another through the pad field.

It shall be understood that the description of the second encapsulatedMSDU 1620 may be superseded by the description of the first encapsulatedMSDU 1610.

It may be assumed that the MPDU 1600 of FIG. 16 is associated with thetransmission queue 1220 of the AC_VO type shown in FIG. 12. Referring toFIG. 16 and Table 1, the user priority level of the first payload (i.e.,MSDU #1) and the user priority level of the second payload (i.e., MSDU#2) may both be set to ‘6’.

In this case, a traffic identifier (TID) corresponding to ‘6’ may beincluded in the MAC header 1601 of the MPDU 1600, which is generatedbased on the first payload (i.e., MSDU #1) and the second payload (i.e.,MSDU #2).

As another example, the user priority level of the first payload (i.e.,MSDU #1) and the user priority level of the second payload (i.e., MSDU#2) may both be set to ‘7’.

In this case, a traffic identifier (TID) corresponding to ‘7’ may beincluded in the MAC header 1601 of the MPDU 1600, which is generatedbased on the first payload (i.e., MSDU #1) and the second payload (i.e.,MSDU #2).

Although it is shown in FIG. 16 that only two encapsulated MSDUs 1610and 1620 are included in the frame body 1602 of FIG. 16, this is merelyexemplary. And therefore, it shall be understood that three or moreencapsulated MSDUs may be included in the frame body 1602 within a rangethat does not exceed the predetermined traffic size.

FIG. 17 is a conceptual view illustrating a frame structure of anA-MPDU, wherein a plurality of MPDUs are aggregated, according to anembodiment.

Referring to FIG. 1 to FIG. 17, the wireless terminal may performencapsulation operations based on a plurality of MPDUs (e.g., MPDU #1,MPDU #2, MPDU #3). Accordingly, first to third encapsulated MPDUs 1701,1702, and 1703 may be generated.

For example, each MPDU (e.g., MPDU #1, MPDU #2, and MPDU #3) may have aframe structure corresponding to the above-described MPDU 1600 of FIG.16.

By logically aggregating a plurality of encapsulated MPDUs 1701, 1702,and 1703 at the bottom of the MAC layer, the wireless device maygenerate an Aggregated-MPDU (A-MPDU) 1700.

More specifically, the first encapsulated MPDU 1701 may further includea first MPDU delimiter (MD #1) field having a predetermined size and afirst pad (Pad #1) field. For example, the first MPDU delimiter (MD #1)field may have a length of 32 bits.

For example, the first MPDU delimiter (MD #1) field may include an EndOf Field (hereinafter referred to as EOF) sub-field, a length sub-fieldbeing allocated with 12 bits, a CRC-8 sub-field being allocated with 8bits, and a signature sub-field being allocated with 8 bits. The CRC-8sub-field may be used for validating the integrity of the first MPDUdelimiter (MD #1) field.

Also, in order to be aligned to a subsequent A-MPDU delimiter field(e.g., MD #2), the Pad field (e.g., Pad #1) may be allocated with avariable length ranging from 0 to 3 bytes. It shall be understood thatthe detailed description of the second encapsulated MPDU 1702 and thethird encapsulated MPDU 1703 may be superseded by the description of thefirst encapsulated MPDU 1701.

The wireless terminal may generate a PPDU 1720 based on a PHY preamble1721 and an A-MPDU 1700. The A-MPDU 1700 may be included in a payloadfield 1722 of the PPDU 1720, which is used for communication that isbased on a physical layer.

All MPDUs (e.g., MPDU #1, MPDU #2, and MPDU #3) being included in theA-MPDU 1700 may be addressed to the same receiver.

Conventionally, only a plurality of MPDUs having the same TID may beaggregated into an A-MPDU 1700. For example, a plurality of MPDUs (e.g.,MPDU #1, MPDU #2, and MPDU #3) included in an A-MPDU 1700 may have thesame TID. That is, a conventional wireless terminal cannot generate oneA-MPDU based on a plurality of MPDUs having different TIDs.

In the present specification, an operation in which a wireless terminalaccording to the IEEE 802.11ax standard generates one A-MPDU based on aplurality of MPDUs having different TIDs may be referred to as amulti-TID A-MPDU aggregation operation.

For example, a wireless terminal according to the IEEE 802.11ax standardmay support a multi-TID A-MPDU aggregation operation. Here, all wirelessterminals according to the IEEE 802.11ax standard may not supportmulti-TID A-MPDU aggregation.

FIG. 18 is a diagram illustrating a field of a basic trigger frameincluding preference information and limit information according to anembodiment.

According to the IEEE 802.11ax standard, the AP may transmit a triggerframe, which individually allocates a plurality of uplink wirelessresource for a plurality of user equipments (or user devices). Thetrigger frame according to the exemplary embodiment of the presentinvention may be interpreted and understood based on the above-describedFIG. 9 to FIG. 11.

For a brief description of FIG. 18, hereinafter, the trigger frame maycorrespond to a trigger frame of a basic type (hereinafter referred toas a ‘basic trigger frame’) for allowing the trigger type field 1060 toperform general triggering.

Furthermore, the basic trigger frame may hereinafter be understood as avariant of the trigger frame of the basic type. The basic trigger framemay further include a trigger dependent user information field 1150 ineach individual user information field 960#1 to 960# N.

A wireless terminal according to the present embodiment may transmit atrigger-based PPDU (hereinafter, “TB PPDU”) in response to a basictrigger frame. The TB PPDU may be understood on the basis of the formatof a PPDU (e.g., 1720) illustrated in FIG. 17. That is, an A-MPDU may beincluded in a payload (e.g., 1722) of the TB PPDU.

A dependent field 1800 of FIG. 18 may correspond to the triggerdependent user information field 1150 included in each individual userinformation field 960#1 to 960# N illustrated in FIG. 9.

The dependent field 1800 may include an MPDU MU Spacing Factor field1810, a TID Aggregation Limit field 1820, a Reserved field 1830, and aPreferred AC field 1840.

The MPDU MU Spacing Factor field 1810 may be used for calculation of avalue multiplied by a minimum MPDU start spacing. For example, the MPDUMU Spacing Factor field 1810 may be allocated two bits.

The TID Aggregation Limit field 1820 according to the present embodimentmay include a value indicating the maximum number of TIDs allowed for anA-MPDU. The TID Aggregation Limit field 1820 may be allocated threebits.

Specifically, a value set in the TID Aggregation Limit field 1820 may beequal to or smaller than “MT+1”. Here, “MT” may be construed as a valueindicated by a Multi-TID Aggregation TX Support sub-field of an HE MACCapabilities Information field of a particular element transmitted by anon-AP STA that is a receiving terminal (t) for which a user informationfield (e.g., 1100 of FIG. 11) is intended. In this case, the Multi-TIDAggregation TX Support sub-field may be set to a value of the number ofTIDs of QoS data frames, which a wireless terminal can transmit via amulti-TID A-MPDU, minus 1.

According to the present embodiment, the wireless terminal may configurean A-MPDU by referring to the TID Aggregation Limit field 1820 of thereceived basic trigger frame.

For example, when the TID Aggregation Limit field 1820 indicates 2, thewireless terminal may support a multi-TID A-MPDU aggregation operation.In this case, the wireless terminal may configure a multi-TID A-MPDUbased on a plurality of MPDUs having up to two types of TIDs.

For example, when the TID Aggregation Limit field 1820 indicates 3, thewireless terminal may support a multi-TID A-MPDU aggregation operation.In this case, the wireless terminal may configure a multi-TID A-MPDUbased on a plurality of MPDUs having up to three types of TIDs.

For example, when the TID Aggregation Limit field 1820 indicates 1, thewireless terminal may configure an A-MPDU based only on a plurality ofMPDUs having one type of TID even though supporting a multi-TID A-MPDUaggregation operation.

That is, when a basic trigger frame with a TID Aggregation Limit fieldset to 1 is received, the wireless terminal may understand that amulti-TID A-MPDU aggregation operation is not allowed.

In the present specification, a case where the TID Aggregation Limitfield 1820 indicates 0 or 1 will be described in detail with referenceto the following drawings.

The Reserved field 1830 may include a one-bit reserved value.

The Preferred AC field 1840 may include preference informationindicating an AC type for an A-MPDU to be configured by the wirelessterminal. For example, values (0 to 3) expressed based on two bits forpreference information may be mapped as below in Table 4.

TABLE 4 Value Description 0 AC_VO 1 AC_VI 2 AC_BE 3 AC_BK

Described is a method in which a wireless terminal configures an A-MPDUincluded in a TB PPDU (HE TB PPDU) in response to a trigger frame when amulti-TID A-MPDU aggregation operation is supported.

For example, a primary AC may refer to an AC type corresponding to atransmission queue about which an internal backoff operation iscompleted first by a wireless terminal among four transmission queuesmapped to four AC types for the wireless terminal one to one. Asecondary AC may refer to the remaining AC types other than the primaryAC.

When all of the following first to third conditions are satisfied, thewireless terminal may configure an A-MPDU based on at least one MPDUcorresponding to the primary AC and at least one MPDU corresponding tothe secondary AC.

According to a first condition, the wireless terminal needs to include,in the A-MPDU, at least one MPDU having a TID corresponding to theprimary AC of a particular TXOP.

According to a second condition, it is assumed that a TXOP limit valuecorresponding to the primary AC is not 0.

According to a third condition, it is assumed that there is no MPDUremaining in a transmission queue corresponding to the primary AC orthat an additional MPDU to be further included is not present in thetransmission queue corresponding to the primary AC.

Basically, when the multi-TID A-MPDU aggregation operation is supported,the wireless terminal may configure an A-MPDU based on a plurality ofMPDUs having the TID corresponding to the primary AC (or a plurality ofMPDUs having a TID corresponding to an AC having a higher priority thanthe primary AC).

Further, when the multi-TID A-MPDU aggregation operation is supported,the wireless terminal may configure a multi-TID A-MPDU within themaximum number of TIDs indicated by the TID Aggregation Limit field1820.

Referring to FIG. 12, FIG. 18, and Table 4, when the Preferred AC field1840 indicates 0, the wireless terminal (e.g., 1200) may include, in aTB PPDU, an A-MPDU generated based on a plurality of MPDUs included in atransmission queue 1220 corresponding to an AC_VO type.

For example, when the Preferred AC field 1840 indicates 1, the wirelessterminal (e.g., 1200) may include, in a TB PPDU, an A-MPDU generatedbased on a plurality of MPDUs 1231, 1232, 1233, and 1234 included in atransmission queue 1230 corresponding to an AC_VI type.

In another example, when the Preferred AC field 1840 indicates 1, thewireless terminal (e.g., 1200) may include, in a TB PPDU, an A-MPDUgenerated based on the plurality of MPDUs 1231, 1232, 1233, and 1234included in the transmission queue 1230 of the AC_VI type and an MPDU1221 included in the transmission queue 1220 of the AC_VO type having ahigher priority than AC_VI.

For example, when the Preferred AC field 1840 indicates 2, the wirelessterminal (e.g., 1200) may include, in a TB PPDU, an A-MPDU generatedbased on a plurality of MPDUs 1241, 1242, and 1243 included in atransmission queue 1240 corresponding to an AC_BE type.

In another example when the Preferred AC field 1840 indicates 2, thewireless terminal (e.g., 1200) may include, in a TB PPDU, an A-MPDUgenerated based on the plurality of MPDUs 1241, 1242, and 1243 includedin the transmission queue 1240 of the AC_BE type and a plurality ofMPDUs 1221, 1231, 1232, 1233, and 1234 included in the transmissionqueues 1220 and 1230 having a higher priority than AC_BE.

For example, when the Preferred AC field 1840 indicates 3, the wirelessterminal (e.g., 1200) may include, in a TB PPDU, an A-MPDU generatedbased on a random frame regardless of the AC type.

Described is a method in which a wireless terminal configures an A-MPDUincluded in a TB PPDU in response to a trigger frame when a multi-TIDA-MPDU aggregation operation is not supported.

Basically, when the multi-TID A-MPDU aggregation operation is notsupported, the wireless terminal may select any one of two TIDscorresponding to an AC type indicated by preference information includedin the Preferred AC field 1840.

For example, when the AC type indicated by the preference informationincluded in the Preferred AC field 1840 is AC_VO, the wireless terminalmay select any one of “6” and “7”, which are TIDs corresponding to theAC_VO type, in order to configure an A-MPDU.

When “7” is selected as a TID, the wireless terminal may include anA-MPDU, in which only MPDUs having a TID of 7 are aggregated among aplurality of MPDU included in a transmission queue corresponding toAC_VO, in a TB PPDU.

Even though the Aggregation Limit field 1820 is set to 1, the wirelessterminal may add an MPDU having a random TID to a pre-generated A-MPDU.

Here, the pre-generated A-MPDU may be generated based on a plurality ofMPDUs having one type of a TID. Here, the MPDU having the random TID maybe a QoS data frame or a QoS null frame that does not requires aseparate response from an AP.

Specifically, an MAC header (e.g., the QoS control field 1518) of theQoS data frame or an MAC header (e.g., the QoS control field 1518) ofthe QoS null frame may include information on an ACK policy of notrequiring a separate response from an AP (hereinafter, referred to as a‘NO ACK policy’) may be included.

Specifically, even though exceeding the maximum number (e.g., one) ofTIDs indicated by the Aggregation Limit field 1820, an MPDU according tothe NO ACK policy may be added to the pre-generated A-MPDU regardless ofthe TID.

For reference, configuring a multi-TID A-MPDU may not be allowed througha Multi-TID Aggregation Support field or an ACK Enabled Multi-TIDSupport field of a HE Capabilities element.

In addition, even though the Preferred AC field 1840 indicates aparticular AC type, the wireless terminal may add an MPDU having arandom TID to a pre-generated A-MPDU.

Here, the pre-generated A-MPDU may be generated based on a plurality ofMPDUs having a particular TID corresponding to a particular AC type.Here, the MPDU having the random TID may be a QoS data frame or a QoSnull frame that does not requires a separate response from an AP.

Specifically, an MAC header (e.g., the QoS control field 1518) of theQoS data frame or an MAC header (e.g., the QoS control field 1518) ofthe QoS null frame may include information on an ACK policy of notrequiring a separate response from an AP may be included.

Further, even though being an MPDU included in an AC type different fromthe AC type indicated by the Preferred AC field 1840 (or an MPDUincluded in an AC type having a lower priority than the AC typeindicated by the preference information), an MPDU according to the NOACK policy may be added to the pre-generated A-MPDU regardless of theTID.

That is, a multi-TID A-MPDU generated based on the MPDU according to theNO ACK policy and the pre-generated A-MPDU may be included in a payloadfield of a TB PPDU (i.e., HE TB PPDU).

The AP needs to individually acknowledge each of a plurality of TIDs ofthe multi-TID A-MPDU. When the multi-TID A-MPDU includes too many typesof TIDs, the performance of the WLAN system may be degraded due tooverheads caused by transmission of ACK frames (or BA frames) foracknowledgment.

However, since the MPDU according to the No ACK policy does not requirea separate acknowledgment operation, the MPDU according to the NO ACKpolicy may be added to the A-MPDU without causing additional overheads.

Although not shown in FIG. 18, an MPDU (e.g., 1500) having a random TIDmay be a QoS Null frame that includes no payload in a frame body field(e.g., 1520).

Referring to Table 3, 9th to 16th bits (bits 8 to 15) of the QoS controlfield 1518 may include queue size information on a transmission queuecorresponding to traffic to be transmitted by an STA.

The queue size information on the transmission queue included in thewireless terminal may be construed as Buffer Status Report (hereinafter,“BSR”) information. For example, an MPDU including BSR information maybe added to a pre-generated A-MPDU regardless of the priority of atransmission queue to which the MPDU belongs.

FIG. 19 illustrates an OFDMA-based random access procedure according toan embodiment. Referring to FIG. 19, the horizontal axis in FIG. 19 mayrepresent time (t). The vertical axis in FIG. 19 may be associated withthe presence of a frame exchanged between an AP and a plurality of STAsin a WLAN system.

For a clear and concise understanding of FIG. 19, it may be assumed thata WLAN system according to the present embodiment includes one AP andfirst to fourth STAs.

In one example, a first STA, a second STA, and a fourth STA may beconstrued as terminals associated with the AP via an associationprocedure. For example, the first STA may have an AID value of 5. Forexample, the second STA may have an AID value of 7. For example, thefourth STA may have an AID value of 3.

In one example, a third STA may be construed as an unassociatedterminal, which has not be subjected to a procedure for association withthe AP.

An OFDMA backoff counter (hereinafter, referred to as an “OBO counter”)may be defined for the first to fourth STAs in FIG. 19. The OBO countermay count down by the resource unit (RU) indicated by a trigger frame.

In addition, an OFDMA contention window (OCW) may be defined for therange of an initial value that can be set in the OBO counter.

For example, the OCW may be defined based on random access informationincluded in a beacon frame periodically transmitted by the AP. Forexample, the random access information may include an OCWmin value forthe OCW.

An STA performing the OFDMA-based random access procedure may set theinitial value of the OBO counter to a random value in a range [0,OCWmin].

For example, an initial OBO value (initial OBO1) set in a OBO counterfor the first STA in FIG. 13 may be 3. For example, an initial OBO value(initial OBO2) set in a OBO counter for the second STA in FIG. 13 may be5. For example, an initial OBO value (initial OBO3) set in a OBO counterfor the third STA in FIG. 13 may be 4. For example, an initial OBO value(initial OBO4) set in a OBO counter for the fourth STA in FIG. 13 may be2.

A trigger frame according to the present embodiment may include aresource unit allocated for the OFDMA-based random access procedure anda resource unit separately allocated for each of a plurality of STAs.Here, the resource unit allocated for the OFDMA-based random accessprocedure may be referred to as an RA resource unit.

The AP of FIG. 19 may transmit a first trigger frame 1910 including aplurality of user information fields (e.g., 960#1 to 960# N in FIG. 9).

For example, a first user information field (e.g., 960#1) may include afirst User Identifier field (e.g., 1110), in which an AID value for anon-AP STA associated with the AP is set to 0, and a first RU Allocationfield (e.g., 1120) indicating a first resource unit (RU1).

For example, a second user information field (e.g., 960#2) may include asecond User Identifier field (e.g., 1110), in which an AID value for anon-AP user STA associated with the AP is set to 0, and a second RUAllocation field (e.g., 1120) indicating a second resource unit (RU2).

For example, a third user information field (e.g., 960#3) may include athird User Identifier field (e.g., 1110), in which an AID value for anon-AP STA associated with the AP is set to 0, and a third RU Allocationfield (e.g., 1120) indicating a third resource unit (RU3).

For example, a fourth user information field (e.g., 960#4) may include afourth User Identifier field (e.g., 1110), in which an AID value for anon-AP STA unassociated with the AP is set to 2045, and a fourth RUAllocation field (e.g., 1120) indicating a fourth resource unit (RU4).

For example, a fifth user information field (e.g., 960#5) may include afifth User Identifier field (e.g., 1110), in which an AID value for anon-AP STA unassociated with the AP is set to 2045, and a fifth RUAllocation field (e.g., 1120) indicating a fifth resource unit (RU5).

For example, a sixth user information field (e.g., 960#6) may include asixth User Identifier field (e.g., 1110), in which an AID value for thefourth STA as a particular non-AP STA associated with the AP is set to3, and a sixth RU Allocation field (e.g., 1120) indicating a sixthresource unit (RU6).

Here, the first to third resource units (RU1, RU2, and RU3 in FIG. 19)may be construed as RA resource units for the non-AP STA associated withthe AP. Further, the fourth and fifth resource units (RU4 and RU5 inFIG. 19) may be construed as RA resource units for the non-AP STAunassociated with the AP.

According to the present embodiment, upon receiving the trigger frame,each STA may perform an OBO countdown operation by the number of RAresource units on the basis of whether the STA is an STA associated withthe AP.

For example, the first STA associated with the AP may determine thefirst to third resource units (RU1 to RU3) included in the receivedfirst trigger frame 1910 as RA resource units. Accordingly, the OBOcounter of the first STA may be updated to a value (‘0’) reduced by ‘3’from the initial OBO value (‘3’) on the basis of the OBO countdownoperation. That is, the first STA may be construed as a terminal thathas completed an OFDMA-based random access backoff procedure.

For example, the second STA associated with the AP may determine thefirst to third resource units (RU1 to RU3) included in the receivedfirst trigger frame 1910 as RA resource units. Accordingly, the OBOcounter of the second STA may be updated to a value (‘2’) reduced by ‘3’from the initial OBO value (‘5’) on the basis of the OBO countdownoperation. Then, the OBO counter of the second STA is maintained at ‘2’.

For example, the third STA unassociated with the AP may determine thefourth and fifth resource units (RU4 and RU5) included in the receivedfirst trigger frame 1910 as RA resource units. Accordingly, the OBOcounter of the third STA may be updated to a value (‘2’) reduced by ‘2’from the initial OBO value (‘4’) on the basis of the OBO countdownoperation. Then, the OBO counter of the third STA is maintained at ‘2’.

For example, the fourth STA associated with the AP is individuallyallocated the sixth resource unit (RU6) through the first trigger frame1910. Accordingly, the fourth STA may maintain the initial OBO value(‘2’) of the OBO counter without performing the OBO countdown operation.

The first STA that has completed the OFDMA-based random access backoffprocedure may randomly select one of the first to third resource units(e.g., RU1, RU2, and RU3 in FIG. 19) allocated through the first triggerframe 1910. For example, the first STA may select the second resourceunit (RU2).

In the present specification, a resource unit selected by the first STAmay be referred to as a random resource unit. After selecting the randomresource unit, a new value may be set in the OBO counter of the firstSTA. For example, it may be assumed that a new value of 4 may be set inthe OBO counter of the first STA.

After the elapse of an SIFS from the transmission of the first triggerframe 1910, a plurality of first uplink frames 1920 may be transmittedfrom the plurality of STAs in response to the first trigger frame 1910.

For example, the plurality of first uplink frames 1920 may include afirst TB PPDU (HE TB PPDU #1), which is transmitted from the first STAon the basis of the second resource unit (RU2), and a second TB PPDU (HETB PPDU #2), which is transmitted from the fourth STA on the basis ofthe sixth resource unit (RU6).

In this case, the first TB PPDU (HE TB PPDU #1) and the second TB PPDU(HE TB PPDU #2) may be transmitted via overlapping time resources on thebasis of OFDMA.

After the elapse of an SIFS from the transmission of the plurality offirst uplink frames 1920, the AP may transmit a first multi-STA blockACK frame 1930 in order to report the successful reception of theplurality of first uplink frames 1920. Here, the details of a multi-STAblock ACK frame are explained with reference to 9.3.1.9.7 of thestandard document IEEE P802.11ax/D2.2, disclosed in February, 2018.

Subsequently, the AP of FIG. 19 may transmit a second trigger frame 1940including a plurality of user information fields (e.g., 960#1 through960# N in FIG. 9).

For example, a first user information field (e.g., 960#1) may include afirst User Identifier field (e.g., 1110), in which an AID value for anon-AP STA associated with the AP is set to 0, and a first RU Allocationfield (e.g., 1120) indicating a first resource unit (RU1).

For example, a second user information field (e.g., 960#2) may include asecond User Identifier field (e.g., 1110), in which an AID value for anon-AP user STA associated with the AP is set to 0, and a second RUAllocation field (e.g., 1120) indicating a second resource unit (RU2).

For example, a third user information field (e.g., 960#3) may include athird User Identifier field (e.g., 1110), in which an AID value for anon-AP STA unassociated with the AP is set to 2045, and a third RUAllocation field (e.g., 1120) indicating a third resource unit (RU3).

For example, a fourth user information field (e.g., 960#4) may include afourth User Identifier field (e.g., 1110), in which an AID value for anon-AP STA unassociated with the AP is set to 2045, and a fourth RUAllocation field (e.g., 1120) indicating a fourth resource unit (RU4).

For example, a fifth user information field (e.g., 960#5) may include afifth User Identifier field (e.g., 1110), in which an AID value for aparticular non-AP STA associated with the AP is set to 6, and a fifth RUAllocation field (e.g., 1120) indicating a fifth resource unit (RU5).

For example, a sixth user information field (e.g., 960#6) may include asixth User Identifier field (e.g., 1110), in which an AID value for aparticular non-AP STA associated with the AP is set to 12, and a sixthRU Allocation field (e.g., 1120) indicating a sixth resource unit (RU6).

Here, the first and second resource units (RU1 and RU2 in FIG. 19) maybe construed as RA resource units for the non-AP STA associated with theAP. Further, the third and fourth resource units (RU4 and RU4 in FIG.19) may be construed as RA resource units for the non-AP STAunassociated with the AP.

For example, the first STA associated with the AP may determine thefirst and second resource units (RU1 and RU2 in FIG. 19) included in thereceived second trigger frame 1940 as RA resource units. Accordingly,the OBO counter of the first STA may be updated to a value (‘2’) reducedby ‘2’ from the initial OBO value (‘4’) on the basis of the OBOcountdown operation. Then, the OBO counter of the first STA ismaintained at ‘2’. For example, the second STA associated with the APmay determine the first and second resource units (RU1 and RU2 in FIG.19) included in the received second trigger frame 1940 as RA resourceunits. Accordingly, the OBO counter of the second STA may be updated toa value (‘0’) reduced by ‘2’ from a resumed OBO value (‘2’) on the basisof the OBO countdown operation. That is, the second STA may be construedas a terminal that has completed an OFDMA-based random access backoffprocedure.

For example, the third STA unassociated with the AP may determine thethird and fourth resource units (RU3 and RU4 in FIG. 19) included in thereceived second trigger frame 1940 as RA resource units. Accordingly,the OBO counter of the third STA may be updated to a value (‘0’) reducedby ‘2’ from a resumed OBO value (‘2’) on the basis of the OBO countdownoperation. That is, the third STA may be construed as a terminal thathas completed an OFDMA-based random access backoff procedure.

For example, the fourth STA unassociated with the AP may determine thethird and fourth resource units (RU3 and RU4 in FIG. 19) included in thereceived second trigger frame 1940 as RA resource units. Accordingly,the OBO counter of the fourth STA may be updated to a value (‘0’)reduced by ‘2’ from a resumed OBO value (‘2’) on the basis of the OBOcountdown operation. That is, the fourth STA may be construed as aterminal that has completed an OFDMA-based random access backoffprocedure.

The second STA that has completed the OFDMA-based random access backoffprocedure may randomly select one of the first and second resource units(e.g., RU1 and RU2 in FIG. 19) allocated through the second triggerframe 1940. For example, the second STA may select the second resourceunit (RU2).

In the present specification, a resource unit selected by the second STAmay be referred to as a random resource unit. After selecting the randomresource unit, a new value may be set in the OBO counter of the secondSTA.

Each of the third STA and the fourth STA that have completed theOFDMA-based random access backoff procedure may randomly select one ofthe third and fourth resource units (e.g., RU3 and RU4 in FIG. 19)allocated through the second trigger frame 1940. For example, the thirdSTA may select the fourth resource unit (RU4), and the fourth STA mayselect the third resource unit (RU3).

After the elapse of an SIFS from the transmission of the second triggerframe 1940, a plurality of second uplink frames 1950 may be transmittedfrom the plurality of STAs in response to the second trigger frame 1940.

For example, the plurality of second uplink frames 1950 may include athird TB PPDU (HE TB PPDU #3), which is transmitted from the fourth STAon the basis of the first resource unit (RU1), a fourth TB PPDU (HE TBPPDU #4), which is transmitted from the second STA on the basis of thesecond resource unit (RU2), and a fifth TB PPDU (HE TB PPDU #5), whichis transmitted from the third STA on the basis of the fourth resourceunit (RU4).

In this case, the third to fifth TB PPDUs (HE TB PPDU #3, HE TB PPDU #4,and HE TB PPDU #5) may be transmitted via overlapping time resources onthe basis of OFDMA.

After the elapse of an SIFS from the transmission of the plurality ofsecond uplink frames 1950, the AP may transmit a second multi-STA blockACK frame 1960 in order to report the successful reception of theplurality of second uplink frames 1950.

It would be understood that the OFDMA-based random access backoffprocedure illustrated in FIG. 19 may be implemented based on the numberof RA resource units included in a trigger frame and the result ofphysical (or logical) carrier sensing of a wireless channel.

However, according to the WLAN system described above, when an uplinkframe including an A-MPDU is transmitted in response to a trigger frame,an MPDU included in an AC of a high priority and an MPDU included in anAC of a relatively low priority may be regarded equally.

Also, when a wireless terminal transmits a TB PPDU in response to atrigger frame, a fairness issue may occur depending on whether thewireless terminal supports a multi-TID A-MPDU aggregation operation.

FIG. 20 is a flowchart illustrating a method for transmitting a triggerframe in a WLAN system according to an embodiment.

Referring to FIG. 1 to FIG. 20, in step S2010, a first wireless terminalmay configure a trigger frame including a plurality of user informationfields for an OFDMA-based random access backoff procedure by a pluralityof second wireless terminals.

For example, the first wireless terminal may correspond to the AP ofFIG. 19. For example, the plurality of second wireless terminals maycorrespond to the first to fourth STAs in FIG. 19.

Each of the plurality of pieces of user information includes resourceallocation information (i.e., 1120 in FIG. 11) for an RA resource unitallocated for the OFDMA-based random access backoff procedure andidentifier information (i.e., 1110 in FIG. 11) that indicates that theRA resource unit is allocated for the OFDMA-based random access backoffprocedure.

Here, an AID value for a wireless terminal associated with the firstwireless terminal among the plurality of second wireless terminals maybe set to 0 in the identifier information. Further, an AID value for awireless terminal unassociated with the first wireless terminal amongthe plurality of second wireless terminals may be set to 2045 in theidentifier information.

That is, it could be understood that the plurality of pieces of userinformation corresponds to the plurality of per user information fields960#1 to 960# N in FIG. 19. In addition, the trigger frame may beconstrued as a basic trigger frame of a basic type. Accordingly, TIDaggregation limit information may be further included in each of theplurality of pieces of user information.

The TID aggregation limit information (i.e., 1820 in FIG. 18) mayindicate the maximum number of TIDs allowed for an A-MPDU generated by asecond wireless terminal that has completed the OFDMA random accessbackoff procedure on the basis of the trigger frame among the pluralityof second wireless terminals.

Here, the plurality of second wireless terminals may include a wirelessterminal that does not support a multi-TID aggregation operation ofaggregating a plurality of MPDUs having different TIDs into one A-MPDU.

When the OFDMA-based random access backoff procedure is performed, thefirst wireless terminal according to the present embodiment may set theTID aggregation limit information (i.e., 1820 in FIG. 18) of the triggerframe to 0 or 1 in order to solve a fairness issue in traffic aboutequally regarding an MPDU included in an AC having a high priority andan MPDU included in an AC having a relatively low priority and to solvea fairness issue about transmission opportunities depending on whetherthe multi-TID A-MPDU aggregation operation is supported.

Here, the A-MPDU may be generated based on a plurality of MPDUs bufferedin the second wireless terminal that has completed the OFDMA randomaccess backoff procedure.

When the TID aggregation limit information is set to 0, the plurality ofMPDUs may include a plurality of control frames that does not solicit animmediate response from the first wireless terminal.

For example, when the TID aggregation limit information is set to 0, theplurality of MPDUs may be construed as one or more QoS null frame oraction frames having the NO ACK policy. In one example, a QoS null framehaving the NO ACK policy may be a BSR frame that indicates the amount oftraffic buffered in a wireless terminal.

When the TID aggregation limit information is set to 0, the transmissionof a QoS data frame using an RA resource unit obtained through the OFDMArandom access backoff procedure is not allowed. Accordingly, a fairnessissue due to priorities of traffic does not occur.

Further, when the TID aggregation limit information is set to 0, thewireless terminal cannot perform the multi-TID A-MPDU aggregationoperation. Accordingly, a fairness issue due to the capabilities ofwireless terminals for the multi-TID A-MPDU aggregation operation doesnot occur.

When the TID aggregation limit information is set to 1, the MPDUstransmitted based on the RA resource unit may include a control framethat solicits an immediate response from the first wireless terminal.

For example, when the TID aggregation limit information is set to 1, theMPDUs may be construed as a QoS null frame that solicits an ACK.

In one example, a QoS null frame that solicits an ACK may be transmittedvia a Single-MPDU (S-MPDU). For example, a QoS null frame that solicitsan ACK may be construed as a frame for a second wireless terminal, whichoperates in a power save mode, to autonomously wake up and to triggerdownlink data, which is buffered in the first wireless terminal, fromthe first wireless terminal.

In another example, the TID aggregation limit information may be set to1 for a wireless terminal that is unassociated with the first wirelessterminal. In this case, the plurality of MPDUs may be construed as amanagement frame transmitted by the unassociated wireless terminal.

When the TID aggregation limit information is set to 1, an A-MPDU isallowed to be generated based on only a plurality of QoS data frameshaving one TID using an RA resource unit obtained through the OFDMArandom access backoff procedure, thus not causing a fairness issue intraffic.

Further, when the TID aggregation limit information is set to 1, thewireless terminal cannot perform the multi-TID A-MPDU aggregationoperation, and thus a fairness issue due to the capabilities of wirelessterminals does not occur do.

In step S2020, the first wireless terminal may transmit the triggerframe configured in step S2010 to the plurality of second wirelessterminals.

Although not shown in FIG. 20, the first wireless terminal may receiveat least one uplink frame from at least one second wireless terminal inresponse to the trigger frame. In this case, the at least one uplinkframe may include at least one A-MPDU generated by the at least onesecond wireless terminal.

For a non-AP STA, the embodiment illustrated in FIG. 20 may be describedas follows. When an RA resource unit is included in a basic triggerframe for an OFDMA-based random access procedure and TID aggregationlimit information corresponding to the RA resource unit is set to 0, thenon-AP STA cannot transmit a QoS data frame or a control frame thatsolicits an immediate response.

According to the present example, when the TID aggregation limitinformation is set to 0, a QoS data frame, the following three optionsmay be provided for the non-AP STA that intends to transmit a QoS dataframe or a control frame that solicits an immediate response (e.g., aPS-Poll frame and a QoS null frame in a S-MPDU).

According to a first option, the non-AP STA may not consider an RAresource unit with TID aggregation limit information set to 0 as aneligible RA resource unit.

Accordingly, the RA resource unit with the TID aggregation limitinformation set to 0 may be excluded from an OBO countdown operation. Inaddition, the RA resource with the TID aggregation limit information setto 0 may not be selected as a random resource unit.

According to a second option, an RA resource unit with TID aggregationlimit information set to 0 may be included in an OBO countdown operationand may be selected as a random resource unit.

However, the non-AP STA may newly select an OBO count value for thenon-AP STA instead of transmitting a QoS data frame based on the RAresource unit with the TID aggregation limit information set to 0.

According to a third option, an RA resource unit with TID aggregationlimit information set to 0 may be included in the OBO countdownoperation but may not be selected as a random resource unit. That is, inthe third option, a random resource unit may be selected only when theTID aggregation limit information is set to 1 in the OFDMA-based randomaccess procedure.

According to the present example, when the TID aggregation limitinformation is set to 1, the non-AP STA may transmit a TB PPDU includingone or more QoS data frames having one TID or a control frame solicitingan immediate response on the basis of a selected random resource unit.

FIG. 21 is a block diagram illustrating a wireless device according toan embodiment.

Referring to FIG. 21, the wireless device may be an STA capable ofimplementing the foregoing embodiments, which may be an AP or a non-APSTA. Further, the wireless device may correspond to the foregoing useror a transmitting terminal that transmits a signal to a user.

As illustrated in FIG. 21, the wireless device includes a processor2110, a memory 2120, and a transceiver 2130. The processor 2110, thememory 2120, and the transceiver 2130 may be configured as separatechips or as a single chip having at least two blocks/functions.

The transceiver 2130 may be a device including a transmitter and areceiver. When a particular operation is performed only any one of thetransmitter and the receiver may operate or both the transmitter and thereceiver may operate. The transceiver 2130 may include one or moreantennas for transmitting and/or receiving a radio signal. Further, thetransceiver 2130 may include an amplifier for amplifying a receptionsignal and/or a transmission signal and a band-pass filter fortransmission on a particular frequency band.

The processor 2110 may implement the functions, processes, and/ormethods proposed in the present specification. For example, theprocessor 2110 may perform operations according to the aforementionedembodiments. That is, the processor 2110 may perform operationsdisclosed in the embodiments of FIG. 1 to FIG. 20.

The processor 2110 may include an application-specific integratedcircuit (ASIC), other chipsets, a logic circuit, a data processor,and/or a converter to convert a baseband signal and a radio signal fromone to the other.

The memory 2120 may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orother storage devices.

FIG. 22 is a block diagram illustrating an example of a device includedin a processor.

Although the example illustrated in FIG. 22 is described with referenceto blocks for a transmission signal for convenience of description, itis obvious that the same blocks may be used to process a receptionsignal.

A data processing unit 2210 generates transmission data (control dataand/or user data) corresponding to a transmission signal. An output fromthe data processing unit 2210 may be input to an encoder 2220. Theencoder 2220 may perform coding using a binary convolutional code (BCC)or a low-density parity-check (LDPC) technique. At least one encoder2220 may be included, and the number of encoders 2220 may be determineddepending on various pieces of information (e.g., the number of datastreams).

An output from the encoder 2220 may be input to an interleaver 2230. Theinterleaver 2230 performs an operation of distributing consecutive bitsignals on radio resources (e.g., time and/or frequency) in order toprevent burst errors due to fading. At least one interleaver 2230 may beincluded, and the number of interleavers 2230 may be determineddepending on various pieces information (e.g., the number of spatialstreams).

An output from the interleaver 2230 may be input to a constellationmapper 2240. The constellation mapper 2240 performs constellationmapping, such as biphase shift keying (BPSK), quadrature phase shiftkeying (QPSK), and n-quadrature amplitude modulation (n-QAM).

An output from the constellation mapper 2240 may be input to a spatialstream encoder 2250. The spatial stream encoder 2250 performs dataprocessing to transmit a transmission signal through at least onespatial stream. For example, the spatial stream encoder 2250 may performat least one of space-time block coding (STBC), cyclic shift diversity(CSD) insertion, and spatial mapping on a transmission signal.

An output from the spatial stream encoder 2250 may be input to a IDFTblock 2260. The IDFT block 2260 performs inverse discrete Fouriertransform (IDFT) or inverse fast Fourier transform (IFFT).

An output from the IDFT block 2260 is input to a guard interval (GI)inserter 2270, and an output from the GI inserter 2270 is input to thetransceiver 2130 of FIG. 21.

Although specific embodiments have been illustrated in the detaileddescription of the present specification, various changes andmodifications are possible within the scope of the presentspecification. Therefore, the scope of the present specification shouldnot be construed as being limited to the foregoing embodiments butshould be determined by the following claims and equivalents thereof.

What is claimed is:
 1. A method in a wireless local area network (WLAN)system, the method comprising: configuring, by a transmitting wirelessterminal, a trigger frame for an orthogonal frequency division multipleaccess (OFDMA)-based random access, wherein the trigger frame includesresource allocation information, identifier information, and trafficidentifier (TID) aggregation limit information, wherein the triggerframe is configured for at least one receiving wireless terminal,wherein a type of the trigger frame is set to a basic type, wherein theresource allocation information includes information related to aresource unit (RU) used for the OFDMA-based random access, wherein theidentifier information is set to an association identifier (AID) of theat least one receiving wireless terminal or one pre-defined value basedon whether the RU is used for the OFDMA-based random access, wherein thetraffic identifier (TID) aggregation limit information includesinformation related to a maximum number of TIDs allowed for an aggregatemedium access control protocol data unit (A-MPDU) to be included in atrigger-based frame to be generated by the at least one receivingwireless terminal, and wherein the TID aggregation limit information isset based on whether the RU is used for the OFDMA-based random access,and the TID aggregation limit information is set to ‘0’ or ‘1’ for theRU being used for the OFDMA-based random access; and transmitting, bythe transmitting wireless terminal, the trigger frame to the at leastone receiving wireless terminal.
 2. The method of claim 1, wherein theat least one receiving wireless terminal is associated with thetransmitting wireless terminal, and the pre-defined value in theidentifier information is set to ‘0’.
 3. The method of claim 1, whereinthe trigger-based frame is a High Efficiency (HE) trigger-based physicalprotocol data unit (PPDU).
 4. The method of claim 1, wherein thetrigger-based frame is received by the transmitting wireless terminalafter transmitting the trigger frame.
 5. The method of claim 1, whereinthe trigger frame further includes preferred access category (AC)information for the trigger-based frame.
 6. A method in a wireless localarea network (WLAN) system, the method comprising: receiving, by areceiving wireless terminal, a trigger frame for an orthogonal frequencydivision multiple access (OFDMA)-based random access from a transmittingwireless terminal, wherein the trigger frame includes resourceallocation information, identifier information, and traffic identifier(TID) aggregation limit information, wherein a type of the trigger frameis set to a basic type, wherein the resource allocation informationincludes information related to a resource unit (RU) used for theOFDMA-based random access, wherein the identifier information is set toan association identifier (AID) of the receiving wireless terminal orone pre-defined value based on whether the RU is used for theOFDMA-based random access, wherein the traffic identifier (TID)aggregation limit information includes information related to a maximumnumber of TIDs allowed for an aggregate medium access control protocoldata unit (A-MPDU) to be included in a trigger-based frame, and whereinthe TID aggregation limit information is set based on whether the RU isused for the OFDMA-based random access, and the TID aggregation limitinformation is set to ‘0’ or ‘1’ for the RU being used for theOFDMA-based random access; configuring, by the receiving wirelessterminal, the trigger-based frame based on the TID aggregation limitinformation; and transmitting, by the receiving wireless terminal, thetrigger-based frame to the transmitting wireless terminal.
 7. The methodof claim 6, wherein the receiving wireless terminal is associated withthe transmitting wireless terminal, and the pre-defined value in theidentifier information is set to ‘0’.
 8. The method of claim 6, whereinthe trigger-based frame is a High Efficiency (HE) trigger-based physicalprotocol data unit (PPDU).
 9. The method of claim 6, wherein the triggerframe further includes preferred access category (AC) information forthe trigger-based frame.
 10. A receiving wireless terminal in a wirelesslocal area network (WLAN) system, comprising: a transceiver configuredfor receiving and transmitting wireless signals; and a processor coupledto the transceiver, wherein the processor is configured to: receive atrigger frame for an orthogonal frequency division multiple access(OFDMA)-based random access from a transmitting wireless terminal,wherein the trigger frame includes resource allocation information,identifier information, and traffic identifier (TID) aggregation limitinformation, wherein a type of the trigger frame is set to a basic type,wherein the resource allocation information includes information relatedto a resource unit (RU) used for the OFDMA-based random access, whereinthe identifier information is set to an association identifier (AID) ofthe receiving wireless terminal or one pre-defined value based onwhether the RU is used for the OFDMA-based random access, wherein thetraffic identifier (TID) aggregation limit information includesinformation related to a maximum number of TIDs allowed for an aggregatemedium access control protocol data unit (A-MPDU) to be included in atrigger-based frame, and wherein the TID aggregation limit informationis set based on whether the RU is used for the OFDMA-based randomaccess, and the TID aggregation limit information is set to ‘0’ or ‘1’for the RU being used for the OFDMA-based random access; configure thetrigger-based frame based on the TID aggregation limit information; andtransmit the trigger-based frame to the transmitting wireless terminal.11. The receiving wireless terminal of claim 10, wherein the receivingwireless terminal is associated with the transmitting wireless terminal,and the pre-defined value in the identifier information is set to ‘0’.12. The receiving wireless terminal of claim 10, wherein thetrigger-based frame is a High Efficiency (HE) trigger-based physicalprotocol data unit (PPDU).
 13. The receiving wireless terminal of claim10, wherein the trigger frame further includes preferred access category(AC) information for the trigger-based frame.